diff --git a/README.md b/README.md
index d008748..b8d6029 100644
--- a/README.md
+++ b/README.md
@@ -623,6 +623,23 @@ gh stack submit
 
 Compared to the typical workflow, there's no need to name branches, run `git add`, or run `git commit` separately. Each `gh stack add -Am "..."` does it all.
 
+## Terminal theme
+
+The interactive screens (`submit`, `modify`, and `view`) automatically adapt their colors to your terminal's background, so they're readable on both dark and light themes. The background is detected from the terminal; if a terminal doesn't report it (some SSH or `tmux` setups), the dark palette is used.
+
+Set `GH_STACK_THEME` to force a palette if detection is wrong:
+
+| Value | Behavior |
+|-------|----------|
+| `auto` (default) | Detect from the terminal background |
+| `light` | Force the light palette |
+| `dark` | Force the dark palette |
+
+```bash
+# Force the light palette for one command
+GH_STACK_THEME=light gh stack view
+```
+
 ## Exit codes
 
 | Code | Meaning |
diff --git a/cmd/root.go b/cmd/root.go
index 0c9e07e..078b51c 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -6,6 +6,7 @@ import (
 	"os"
 
 	"github.com/github/gh-stack/internal/config"
+	"github.com/github/gh-stack/internal/tui/shared"
 	"github.com/spf13/cobra"
 )
 
@@ -35,6 +36,12 @@ locally, then push to GitHub to create your stack of PRs.`,
 		Version:       Version,
 		SilenceUsage:  true,
 		SilenceErrors: true,
+		// Honor GH_STACK_THEME (auto|light|dark) before any command renders, so
+		// the background-aware TUI palette can be forced when a terminal
+		// mis-detects its background.
+		PersistentPreRun: func(_ *cobra.Command, _ []string) {
+			shared.ApplyThemeOverride()
+		},
 	}
 
 	root.SetVersionTemplate("gh stack version {{.Version}}\n")
diff --git a/docs/src/content/docs/reference/cli.md b/docs/src/content/docs/reference/cli.md
index ce2d268..6227d01 100644
--- a/docs/src/content/docs/reference/cli.md
+++ b/docs/src/content/docs/reference/cli.md
@@ -586,6 +586,19 @@ gh stack feedback "Support for reordering branches"
 
 ---
 
+## Environment Variables
+
+| Variable | Values | Description |
+|----------|--------|-------------|
+| `GH_STACK_THEME` | `auto` (default), `light`, `dark` | Controls the color palette of the interactive screens (`submit`, `modify`, `view`). They adapt to your terminal background automatically; set this to force the light or dark palette when a terminal doesn't report its background (some SSH or `tmux` setups). |
+
+```sh
+# Force the light palette for one command
+GH_STACK_THEME=light gh stack view
+```
+
+---
+
 ## Exit Codes
 
 | Code | Meaning |
diff --git a/internal/tui/modifyview/model.go b/internal/tui/modifyview/model.go
index 839ad86..314232c 100644
--- a/internal/tui/modifyview/model.go
+++ b/internal/tui/modifyview/model.go
@@ -1465,7 +1465,7 @@ func (m Model) buildHeaderConfig() shared.HeaderConfig {
 		{Icon: "○", Label: branchInfo},
 	}
 	if pendingSummary != "" {
-		yellowStyle := lipgloss.NewStyle().Foreground(lipgloss.Color("3"))
+		yellowStyle := lipgloss.NewStyle().Foreground(shared.ColorYellow)
 		infoLines = append(infoLines, shared.HeaderInfoLine{Icon: "■", Label: pendingSummary, IconStyle: &yellowStyle})
 	} else {
 		infoLines = append(infoLines, shared.HeaderInfoLine{Icon: "□", Label: "No pending changes"})
diff --git a/internal/tui/modifyview/styles.go b/internal/tui/modifyview/styles.go
index 4435902..caabf5d 100644
--- a/internal/tui/modifyview/styles.go
+++ b/internal/tui/modifyview/styles.go
@@ -1,42 +1,48 @@
 package modifyview
 
-import "github.com/charmbracelet/lipgloss"
+import (
+	"github.com/charmbracelet/lipgloss"
 
+	"github.com/github/gh-stack/internal/tui/shared"
+)
+
+// Colors come from the background-aware palette in internal/tui/shared so the
+// modify view reads well on both dark and light terminals.
 var (
 	// Action annotation styles (modify-specific)
-	dropBadge   = lipgloss.NewStyle().Foreground(lipgloss.Color("1"))  // red
-	foldBadge   = lipgloss.NewStyle().Foreground(lipgloss.Color("3"))  // yellow
-	renameBadge = lipgloss.NewStyle().Foreground(lipgloss.Color("14")) // cyan
-	moveBadge   = lipgloss.NewStyle().Foreground(lipgloss.Color("5"))  // magenta/purple
-	insertBadge = lipgloss.NewStyle().Foreground(lipgloss.Color("2"))  // green
+	dropBadge   = lipgloss.NewStyle().Foreground(shared.ColorRed)    // drop
+	foldBadge   = lipgloss.NewStyle().Foreground(shared.ColorYellow) // fold
+	renameBadge = lipgloss.NewStyle().Foreground(shared.ColorAccent) // rename
+	moveBadge   = lipgloss.NewStyle().Foreground(shared.ColorPurple) // move
+	insertBadge = lipgloss.NewStyle().Foreground(shared.ColorGreen)  // insert
 
 	// Branch name overrides for drop/fold/insert
-	dropBranchStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("1")).Strikethrough(true) // red strikethrough
-	foldBranchStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("3")).Strikethrough(true) // yellow strikethrough
-	insertBranchStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("2"))                     // green
+	dropBranchStyle   = lipgloss.NewStyle().Foreground(shared.ColorRed).Strikethrough(true)
+	foldBranchStyle   = lipgloss.NewStyle().Foreground(shared.ColorYellow).Strikethrough(true)
+	insertBranchStyle = lipgloss.NewStyle().Foreground(shared.ColorGreen)
 
 	// Connector color overrides for drop/fold/move/insert
-	dropConnectorStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("1")) // red
-	foldConnectorStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("3")) // yellow
-	movedConnectorStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("5")) // magenta/purple
-	insertConnectorStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("2")) // green
+	dropConnectorStyle   = lipgloss.NewStyle().Foreground(shared.ColorRed)
+	foldConnectorStyle   = lipgloss.NewStyle().Foreground(shared.ColorYellow)
+	movedConnectorStyle  = lipgloss.NewStyle().Foreground(shared.ColorPurple)
+	insertConnectorStyle = lipgloss.NewStyle().Foreground(shared.ColorGreen)
 
 	// Status line styles
-	statusBarStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	statusCountStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true)
-	statusKeyStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("14"))
-	statusDescStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	statusBarStyle   = lipgloss.NewStyle().Foreground(shared.ColorTextMuted)
+	statusCountStyle = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true)
+	statusKeyStyle   = lipgloss.NewStyle().Foreground(shared.ColorAccent)
+	statusDescStyle  = lipgloss.NewStyle().Foreground(shared.ColorTextMuted)
 
 	// Help overlay styles
 	helpOverlayStyle = lipgloss.NewStyle().
 				Border(lipgloss.RoundedBorder()).
-				BorderForeground(lipgloss.Color("8")).
+				BorderForeground(shared.ColorBorder).
 				Padding(1, 2)
-	helpKeyStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("14")).Bold(true)
-	helpDescStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("15"))
-	helpTitleStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true).Underline(true)
+	helpKeyStyle   = lipgloss.NewStyle().Foreground(shared.ColorAccent).Bold(true)
+	helpDescStyle  = lipgloss.NewStyle().Foreground(shared.ColorText)
+	helpTitleStyle = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true).Underline(true)
 
 	// Transient message styles
-	transientErrorStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("1")) // red
-	transientInfoStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("8")) // gray
+	transientErrorStyle = lipgloss.NewStyle().Foreground(shared.ColorRed)
+	transientInfoStyle  = lipgloss.NewStyle().Foreground(shared.ColorTextMuted)
 )
diff --git a/internal/tui/shared/header.go b/internal/tui/shared/header.go
index e00ac14..b40e27a 100644
--- a/internal/tui/shared/header.go
+++ b/internal/tui/shared/header.go
@@ -361,7 +361,7 @@ func RenderHeader(b *strings.Builder, cfg HeaderConfig, width, height int) {
 }
 
 // disabledShortcutStyle renders both key and desc in dim gray.
-var disabledShortcutStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("240"))
+var disabledShortcutStyle = lipgloss.NewStyle().Foreground(ColorTextFaint)
 
 // renderShortcutEntry renders a single shortcut, dimmed if disabled.
 func renderShortcutEntry(sc ShortcutEntry) string {
diff --git a/internal/tui/shared/render.go b/internal/tui/shared/render.go
index af594a9..94912a1 100644
--- a/internal/tui/shared/render.go
+++ b/internal/tui/shared/render.go
@@ -88,16 +88,16 @@ func ResolveConnectorStyle(node BranchNodeData, isFocused bool) (string, lipglos
 // StatusIcon returns the appropriate status icon for a branch.
 func StatusIcon(node BranchNodeData) string {
 	if node.Ref.IsMerged() {
-		return MergedIcon
+		return mergedIconStyle.Render(mergedGlyph)
 	}
 	if node.Ref.IsQueued() {
-		return QueuedIcon
+		return queuedIconStyle.Render(queuedGlyph)
 	}
 	if !node.IsLinear {
-		return WarningIcon
+		return warningIconStyle.Render(warningGlyph)
 	}
 	if node.PR != nil && node.PR.Number != 0 {
-		return OpenIcon
+		return openIconStyle.Render(openGlyph)
 	}
 	return ""
 }
diff --git a/internal/tui/shared/styles.go b/internal/tui/shared/styles.go
index f3a4430..b5ddba8 100644
--- a/internal/tui/shared/styles.go
+++ b/internal/tui/shared/styles.go
@@ -4,52 +4,59 @@ import "github.com/charmbracelet/lipgloss"
 
 var (
 	// Branch name styles
-	CurrentBranchStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("14")).Bold(true)
-	NormalBranchStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("15"))
-	MergedBranchStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	TrunkStyle         = lipgloss.NewStyle().Foreground(lipgloss.Color("8")).Italic(true)
+	CurrentBranchStyle = lipgloss.NewStyle().Foreground(ColorAccent).Bold(true)
+	NormalBranchStyle  = lipgloss.NewStyle().Foreground(ColorText)
+	MergedBranchStyle  = lipgloss.NewStyle().Foreground(ColorTextMuted)
+	TrunkStyle         = lipgloss.NewStyle().Foreground(ColorTextMuted).Italic(true)
 
-	// Status indicators
-	MergedIcon  = lipgloss.NewStyle().Foreground(lipgloss.Color("5")).Render("✓")
-	WarningIcon = lipgloss.NewStyle().Foreground(lipgloss.Color("3")).Render("⚠")
-	OpenIcon    = lipgloss.NewStyle().Foreground(lipgloss.Color("2")).Render("○")
-	QueuedIcon  = lipgloss.NewStyle().Foreground(lipgloss.Color("130")).Render("◎")
+	// Status indicator glyphs. These are rendered at use-time (see StatusIcon)
+	// with the styles below so their adaptive colors resolve against the detected
+	// terminal background rather than being baked in at package-init time.
+	mergedGlyph  = "✓"
+	warningGlyph = "⚠"
+	openGlyph    = "○"
+	queuedGlyph  = "◎"
+
+	mergedIconStyle  = lipgloss.NewStyle().Foreground(ColorPurple)
+	warningIconStyle = lipgloss.NewStyle().Foreground(ColorYellow)
+	openIconStyle    = lipgloss.NewStyle().Foreground(ColorGreen)
+	queuedIconStyle  = lipgloss.NewStyle().Foreground(ColorYellow)
 
 	// PR status styles
-	PRLinkStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Underline(true)
-	PROpenStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("2"))
-	PRMergedStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("5"))
-	PRClosedStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("1"))
-	PRDraftStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	PRQueuedStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("130"))
+	PRLinkStyle   = lipgloss.NewStyle().Foreground(ColorText).Underline(true)
+	PROpenStyle   = lipgloss.NewStyle().Foreground(ColorGreen)
+	PRMergedStyle = lipgloss.NewStyle().Foreground(ColorPurple)
+	PRClosedStyle = lipgloss.NewStyle().Foreground(ColorRed)
+	PRDraftStyle  = lipgloss.NewStyle().Foreground(ColorGray)
+	PRQueuedStyle = lipgloss.NewStyle().Foreground(ColorYellow)
 
 	// Diff stats
-	AdditionsStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("2"))
-	DeletionsStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("1"))
+	AdditionsStyle = lipgloss.NewStyle().Foreground(ColorGreen)
+	DeletionsStyle = lipgloss.NewStyle().Foreground(ColorRed)
 
 	// Commit lines
-	CommitSHAStyle     = lipgloss.NewStyle().Foreground(lipgloss.Color("3"))
-	CommitSubjectStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("15"))
-	CommitTimeStyle    = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	CommitSHAStyle     = lipgloss.NewStyle().Foreground(ColorYellow)
+	CommitSubjectStyle = lipgloss.NewStyle().Foreground(ColorText)
+	CommitTimeStyle    = lipgloss.NewStyle().Foreground(ColorTextMuted)
 
 	// Connector lines
-	ConnectorStyle        = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	ConnectorDashedStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("3"))
-	ConnectorFocusedStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("15"))
-	ConnectorCurrentStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("14"))
-	ConnectorMergedStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("5"))
-	ConnectorQueuedStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("130"))
+	ConnectorStyle        = lipgloss.NewStyle().Foreground(ColorBorder)
+	ConnectorDashedStyle  = lipgloss.NewStyle().Foreground(ColorYellow)
+	ConnectorFocusedStyle = lipgloss.NewStyle().Foreground(ColorText)
+	ConnectorCurrentStyle = lipgloss.NewStyle().Foreground(ColorAccent)
+	ConnectorMergedStyle  = lipgloss.NewStyle().Foreground(ColorPurple)
+	ConnectorQueuedStyle  = lipgloss.NewStyle().Foreground(ColorYellow)
 
 	// Dim text
-	DimStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("240"))
+	DimStyle = lipgloss.NewStyle().Foreground(ColorTextFaint)
 
 	// Header styles
-	HeaderBorderStyle    = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	HeaderTitleStyle     = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true)
-	HeaderInfoStyle      = lipgloss.NewStyle().Foreground(lipgloss.Color("14"))
-	HeaderInfoLabelStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	HeaderShortcutKey    = lipgloss.NewStyle().Foreground(lipgloss.Color("15"))
-	HeaderShortcutDesc   = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	HeaderBorderStyle    = lipgloss.NewStyle().Foreground(ColorBorder)
+	HeaderTitleStyle     = lipgloss.NewStyle().Foreground(ColorText).Bold(true)
+	HeaderInfoStyle      = lipgloss.NewStyle().Foreground(ColorAccent)
+	HeaderInfoLabelStyle = lipgloss.NewStyle().Foreground(ColorTextMuted)
+	HeaderShortcutKey    = lipgloss.NewStyle().Foreground(ColorText)
+	HeaderShortcutDesc   = lipgloss.NewStyle().Foreground(ColorTextMuted)
 
 	// Expand/collapse icons
 	ExpandedIcon  = "▾"
diff --git a/internal/tui/shared/theme.go b/internal/tui/shared/theme.go
new file mode 100644
index 0000000..0cb51ad
--- /dev/null
+++ b/internal/tui/shared/theme.go
@@ -0,0 +1,86 @@
+package shared
+
+import (
+	"os"
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+// This file defines the shared, background-aware color palette used by every
+// gh-stack TUI (submit, view, modify).
+//
+// Colors are expressed as lipgloss.AdaptiveColor, whose Light/Dark variant is
+// chosen at render time from the terminal's detected background. Bubble Tea
+// triggers that detection once at startup (see bubbletea/tea_init.go), so the
+// right variant is picked automatically; terminals that don't answer the query
+// fall back to the dark palette, preserving the original look.
+//
+// Values are truecolor hex (GitHub Primer-inspired) rather than ANSI palette
+// indices so they render consistently across themes — notably solarized, which
+// repurposes ANSI 8–15 as background tones. lipgloss downsamples to the nearest
+// ANSI color on terminals without truecolor support.
+var (
+	// ColorText is primary/emphasis ink: titles, branch names, links, active
+	// keys, the description scrollbar thumb.
+	ColorText = lipgloss.AdaptiveColor{Dark: "#f0f6fc", Light: "#1f2328"}
+	// ColorTextMuted is secondary ink and dim chrome text: section labels,
+	// shortcut descriptions, hints, trunk/merged branches, timestamps.
+	ColorTextMuted = lipgloss.AdaptiveColor{Dark: "#9198a1", Light: "#59636e"}
+	// ColorTextFaint is disabled/de-emphasized ink: skipped branches, disabled
+	// shortcuts.
+	ColorTextFaint = lipgloss.AdaptiveColor{Dark: "#656c76", Light: "#818b98"}
+
+	// ColorBorder is structural chrome: panel borders, tree connectors, the
+	// vertical spine, horizontal rules, scrollbar tracks, segmented-control frame.
+	ColorBorder = lipgloss.AdaptiveColor{Dark: "#3d444d", Light: "#d1d9e0"}
+	// ColorRowShade tints the focused (currently-viewed) row's background in the
+	// left timeline. A neutral wash that reads as a subtle highlight on either
+	// background — light gray on light terminals, and a lifted slate on dark
+	// terminals so it stays visible against near-black backgrounds.
+	ColorRowShade = lipgloss.AdaptiveColor{Dark: "#353941", Light: "#eaeef2"}
+
+	// ColorAccent is interactive emphasis: the current/focused branch, keyboard
+	// shortcut keys, footer accents.
+	ColorAccent = lipgloss.AdaptiveColor{Dark: "#2dd4bf", Light: "#0a7ea4"}
+
+	// Semantic status colors, mirroring how GitHub colors PR states. Reused for
+	// diff stats (green/red), commit SHAs and warnings (yellow), and modify
+	// action badges.
+	ColorBlue   = lipgloss.AdaptiveColor{Dark: "#4493f8", Light: "#0969da"} // NEW
+	ColorGreen  = lipgloss.AdaptiveColor{Dark: "#3fb950", Light: "#1a7f37"} // OPEN, additions, insert
+	ColorGray   = lipgloss.AdaptiveColor{Dark: "#9198a1", Light: "#59636e"} // DRAFT
+	ColorYellow = lipgloss.AdaptiveColor{Dark: "#d29922", Light: "#9a6700"} // QUEUED, warning, commit SHA, fold
+	ColorPurple = lipgloss.AdaptiveColor{Dark: "#bc8cff", Light: "#8250df"} // MERGED, move
+	ColorRed    = lipgloss.AdaptiveColor{Dark: "#f85149", Light: "#cf222e"} // CLOSED, deletions, drop, errors
+
+	// ColorOnFill is text drawn on top of a solid colored fill (e.g. the green
+	// "selected" pill): near-black on the lighter dark-mode fills, white on the
+	// darker light-mode fills.
+	ColorOnFill = lipgloss.AdaptiveColor{Dark: "#0d1117", Light: "#ffffff"}
+
+	// ColorButtonFg/ColorButtonBg style the prominent inverted action button
+	// (e.g. submit). The background inverts against the terminal so the button
+	// stays prominent in both modes.
+	ColorButtonBg = lipgloss.AdaptiveColor{Dark: "#f0f6fc", Light: "#1f2328"}
+	ColorButtonFg = lipgloss.AdaptiveColor{Dark: "#0d1117", Light: "#ffffff"}
+)
+
+// ApplyThemeOverride honors the GH_STACK_THEME environment variable, forcing the
+// light or dark palette regardless of what the terminal reports. It must be
+// called before the first render (e.g. before launching a Bubble Tea program).
+//
+//	GH_STACK_THEME=light  force the light palette
+//	GH_STACK_THEME=dark   force the dark palette
+//	GH_STACK_THEME=auto   (or unset) detect from the terminal background
+//
+// Use this for terminals that don't answer the background query (some SSH/tmux
+// setups) and therefore mis-detect.
+func ApplyThemeOverride() {
+	switch strings.ToLower(strings.TrimSpace(os.Getenv("GH_STACK_THEME"))) {
+	case "light":
+		lipgloss.SetHasDarkBackground(false)
+	case "dark":
+		lipgloss.SetHasDarkBackground(true)
+	}
+}
diff --git a/internal/tui/shared/theme_test.go b/internal/tui/shared/theme_test.go
new file mode 100644
index 0000000..ab5279d
--- /dev/null
+++ b/internal/tui/shared/theme_test.go
@@ -0,0 +1,74 @@
+package shared
+
+import (
+	"io"
+	"testing"
+
+	"github.com/charmbracelet/lipgloss"
+	"github.com/muesli/termenv"
+	"github.com/stretchr/testify/assert"
+)
+
+// TestPaletteIsBackgroundAware verifies that the palette's adaptive colors
+// resolve to different output under a light vs dark background. It uses a local
+// renderer with a color-capable profile so it doesn't mutate global state.
+func TestPaletteIsBackgroundAware(t *testing.T) {
+	colors := map[string]lipgloss.AdaptiveColor{
+		"text":      ColorText,
+		"textMuted": ColorTextMuted,
+		"textFaint": ColorTextFaint,
+		"border":    ColorBorder,
+		"accent":    ColorAccent,
+		"green":     ColorGreen,
+		"red":       ColorRed,
+		"buttonBg":  ColorButtonBg,
+	}
+
+	for name, c := range colors {
+		t.Run(name, func(t *testing.T) {
+			r := lipgloss.NewRenderer(io.Discard)
+			r.SetColorProfile(termenv.TrueColor)
+
+			r.SetHasDarkBackground(true)
+			dark := r.NewStyle().Foreground(c).Render("x")
+			r.SetHasDarkBackground(false)
+			light := r.NewStyle().Foreground(c).Render("x")
+
+			assert.NotEqual(t, dark, light, "%s should differ between dark and light backgrounds", name)
+		})
+	}
+}
+
+func TestApplyThemeOverride(t *testing.T) {
+	// ApplyThemeOverride mutates the default renderer; restore it afterwards.
+	before := lipgloss.HasDarkBackground()
+	t.Cleanup(func() { lipgloss.SetHasDarkBackground(before) })
+
+	t.Run("light forces a light background", func(t *testing.T) {
+		lipgloss.SetHasDarkBackground(true)
+		t.Setenv("GH_STACK_THEME", "light")
+		ApplyThemeOverride()
+		assert.False(t, lipgloss.HasDarkBackground())
+	})
+
+	t.Run("dark forces a dark background", func(t *testing.T) {
+		lipgloss.SetHasDarkBackground(false)
+		t.Setenv("GH_STACK_THEME", "dark")
+		ApplyThemeOverride()
+		assert.True(t, lipgloss.HasDarkBackground())
+	})
+
+	t.Run("auto leaves the detected value unchanged", func(t *testing.T) {
+		lipgloss.SetHasDarkBackground(true)
+		t.Setenv("GH_STACK_THEME", "auto")
+		ApplyThemeOverride()
+		assert.True(t, lipgloss.HasDarkBackground())
+	})
+
+	t.Run("unset leaves the detected value unchanged", func(t *testing.T) {
+		lipgloss.SetHasDarkBackground(false)
+		t.Setenv("GH_STACK_THEME", "")
+		ApplyThemeOverride()
+		assert.False(t, lipgloss.HasDarkBackground())
+	})
+}
diff --git a/internal/tui/submitview/editor.go b/internal/tui/submitview/editor.go
index c4d6d92..c394450 100644
--- a/internal/tui/submitview/editor.go
+++ b/internal/tui/submitview/editor.go
@@ -6,6 +6,8 @@ import (
 
 	"github.com/charmbracelet/bubbles/textarea"
 	"github.com/charmbracelet/lipgloss"
+
+	"github.com/github/gh-stack/internal/tui/shared"
 )
 
 // currentNode returns a pointer to the focused node, or nil.
@@ -266,9 +268,9 @@ func descTextWidth(innerW int) int {
 // so the scrollbar (the content's last column) sits flush against the right
 // border with no extra margin.
 func descBox(content string, width int, focused bool) string {
-	bc := lipgloss.Color("8")
+	var bc lipgloss.TerminalColor = shared.ColorBorder
 	if focused {
-		bc = lipgloss.Color("14")
+		bc = shared.ColorAccent
 	}
 	w := width - 2
 	if w < 1 {
@@ -557,9 +559,9 @@ func (m Model) draftSegmentBounds() (segStart, dividerX, segEnd int) {
 // fieldBox wraps a field's content in a rounded box whose border highlights when
 // focused. width is the desired outer width.
 func fieldBox(content string, width int, focused bool) string {
-	bc := lipgloss.Color("8")
+	var bc lipgloss.TerminalColor = shared.ColorBorder
 	if focused {
-		bc = lipgloss.Color("14")
+		bc = shared.ColorAccent
 	}
 	w := width - 2
 	if w < 1 {
diff --git a/internal/tui/submitview/help.go b/internal/tui/submitview/help.go
index 21561aa..ef85f0d 100644
--- a/internal/tui/submitview/help.go
+++ b/internal/tui/submitview/help.go
@@ -4,17 +4,19 @@ import (
 	"strings"
 
 	"github.com/charmbracelet/lipgloss"
+
+	"github.com/github/gh-stack/internal/tui/shared"
 )
 
 var (
 	helpOverlayStyle = lipgloss.NewStyle().
 				Border(lipgloss.RoundedBorder()).
-				BorderForeground(lipgloss.Color("8")).
+				BorderForeground(shared.ColorBorder).
 				Padding(1, 2)
-	helpTitleStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true).Underline(true)
-	helpSectionStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("14")).Bold(true)
-	helpKeyStyle     = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true)
-	helpDescStyle    = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	helpTitleStyle   = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true).Underline(true)
+	helpSectionStyle = lipgloss.NewStyle().Foreground(shared.ColorAccent).Bold(true)
+	helpKeyStyle     = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true)
+	helpDescStyle    = lipgloss.NewStyle().Foreground(shared.ColorTextMuted)
 )
 
 // helpEntry is a single key/description pair in the help overlay.
diff --git a/internal/tui/submitview/preview.go b/internal/tui/submitview/preview.go
index 8a2e17f..7ba03f6 100644
--- a/internal/tui/submitview/preview.go
+++ b/internal/tui/submitview/preview.go
@@ -8,6 +8,7 @@ import (
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/glamour"
 	"github.com/charmbracelet/glamour/styles"
+	"github.com/charmbracelet/lipgloss"
 )
 
 // editorFinishedMsg is delivered after the external $EDITOR process exits.
@@ -117,10 +118,12 @@ func writeTempDescription(content string) (string, error) {
 }
 
 // renderMarkdown renders markdown to styled terminal output using Glamour. It
-// uses a fixed dark style rather than glamour.WithAutoStyle(): auto-style probes
-// the terminal background with an OSC query whose response is consumed by Bubble
-// Tea's own input reader, so the query blocks forever and freezes the UI. On any
-// error it falls back to the raw markdown so the user still sees their content.
+// selects the light or dark Glamour style from the already-detected terminal
+// background (lipgloss.HasDarkBackground, cached at startup) rather than
+// glamour.WithAutoStyle(): auto-style probes the terminal with an OSC query whose
+// response is consumed by Bubble Tea's own input reader, so the query blocks
+// forever and freezes the UI. On any error it falls back to the raw markdown so
+// the user still sees their content.
 func renderMarkdown(md string, width int) string {
 	if strings.TrimSpace(md) == "" {
 		return hintStyle.Render("(no description)")
@@ -128,11 +131,15 @@ func renderMarkdown(md string, width int) string {
 	if width < 10 {
 		width = 10
 	}
-	// Use glamour's "dark" style but drop the document block's default 2-column
-	// margin so the preview text aligns flush-left with the edit-mode textarea
-	// instead of being indented. Copying the struct and replacing the Margin
-	// pointer leaves the shared package-level style untouched.
+	// Match the preview to the terminal background, then drop the document
+	// block's default 2-column margin so the preview text aligns flush-left with
+	// the edit-mode textarea instead of being indented. Copying the struct and
+	// replacing the Margin pointer leaves the shared package-level style
+	// untouched.
 	style := styles.DarkStyleConfig
+	if !lipgloss.HasDarkBackground() {
+		style = styles.LightStyleConfig
+	}
 	var noMargin uint
 	style.Document.Margin = &noMargin
 	r, err := glamour.NewTermRenderer(
diff --git a/internal/tui/submitview/render.go b/internal/tui/submitview/render.go
index 5d9233a..ca92585 100644
--- a/internal/tui/submitview/render.go
+++ b/internal/tui/submitview/render.go
@@ -10,7 +10,7 @@ import (
 
 // Chrome styles shared across the submit views.
 var (
-	stackInfoStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	stackInfoStyle = lipgloss.NewStyle().Foreground(shared.ColorTextMuted)
 )
 
 // headerHeight returns the number of screen rows the shared header occupies, or
@@ -56,7 +56,7 @@ func (m Model) buildHeaderConfig() shared.HeaderConfig {
 		}
 	}
 	if newCount > 0 {
-		yellowStyle := lipgloss.NewStyle().Foreground(lipgloss.Color("3"))
+		yellowStyle := lipgloss.NewStyle().Foreground(shared.ColorYellow)
 		prWord := "PRs"
 		if newCount == 1 {
 			prWord = "PR"
diff --git a/internal/tui/submitview/screen.go b/internal/tui/submitview/screen.go
index 011ae3f..f1c35b6 100644
--- a/internal/tui/submitview/screen.go
+++ b/internal/tui/submitview/screen.go
@@ -661,7 +661,7 @@ func leftPanelBox(content string, width, height int) string {
 	}
 	return lipgloss.NewStyle().
 		Border(lipgloss.RoundedBorder()).
-		BorderForeground(lipgloss.Color("8")).
+		BorderForeground(shared.ColorBorder).
 		Width(innerW).
 		Height(innerH).
 		MaxHeight(height).
@@ -777,30 +777,30 @@ func (m Model) branchCircle(n SubmitNode, focused bool) string {
 	glyph, color := "○", n.State.Color()
 	switch {
 	case n.State == StateNew && n.Included:
-		glyph, color = "●", lipgloss.Color("14") // filled cyan
+		glyph, color = "●", lipgloss.TerminalColor(shared.ColorAccent) // filled accent
 	case n.State == StateNew:
-		glyph, color = "◌", lipgloss.Color("245") // dotted ring: skipped
+		glyph, color = "◌", lipgloss.TerminalColor(shared.ColorTextFaint) // dotted ring: skipped
 	}
 	return bgIf(lipgloss.NewStyle().Foreground(color), focused).Render(glyph)
 }
 
-// branchNameStyle returns the full-name style: white and bold for a branch that
-// will become a PR, muted gray for skipped or existing-PR branches.
+// branchNameStyle returns the full-name style: primary and bold for a branch that
+// will become a PR, muted for skipped or existing-PR branches.
 func (m Model) branchNameStyle(n SubmitNode, focused bool) lipgloss.Style {
-	st := lipgloss.NewStyle().Foreground(lipgloss.Color("245"))
+	st := lipgloss.NewStyle().Foreground(shared.ColorTextMuted)
 	if n.State == StateNew && n.Included {
-		st = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true)
+		st = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true)
 	}
 	return bgIf(st, focused)
 }
 
-// branchCheckbox renders a NEW branch's include checkbox: cyan [x] when included,
-// gray [ ] when skipped.
+// branchCheckbox renders a NEW branch's include checkbox: accent [x] when
+// included, muted [ ] when skipped.
 func (m Model) branchCheckbox(n SubmitNode, focused bool) string {
 	if n.Included {
-		return bgIf(lipgloss.NewStyle().Foreground(lipgloss.Color("14")), focused).Render("[x]")
+		return bgIf(lipgloss.NewStyle().Foreground(shared.ColorAccent), focused).Render("[x]")
 	}
-	return bgIf(lipgloss.NewStyle().Foreground(lipgloss.Color("8")), focused).Render("[ ]")
+	return bgIf(lipgloss.NewStyle().Foreground(shared.ColorTextMuted), focused).Render("[ ]")
 }
 
 // branchMetaLine renders an existing PR's "state · #num" line, the state word in
diff --git a/internal/tui/submitview/styles.go b/internal/tui/submitview/styles.go
index a691c38..77e7603 100644
--- a/internal/tui/submitview/styles.go
+++ b/internal/tui/submitview/styles.go
@@ -1,26 +1,32 @@
 package submitview
 
-import "github.com/charmbracelet/lipgloss"
-
-// State foreground colors, matching how GitHub.com colors these PR states.
-var stateColors = map[BranchState]lipgloss.Color{
-	StateNew:    lipgloss.Color("4"),   // blue
-	StateOpen:   lipgloss.Color("2"),   // green
-	StateDraft:  lipgloss.Color("250"), // gray
-	StateQueued: lipgloss.Color("137"), // brown
-	StateMerged: lipgloss.Color("5"),   // purple
-	StateClosed: lipgloss.Color("1"),   // red
+import (
+	"github.com/charmbracelet/lipgloss"
+
+	"github.com/github/gh-stack/internal/tui/shared"
+)
+
+// State foreground colors, matching how GitHub.com colors these PR states. Each
+// is background-aware (see internal/tui/shared/theme.go).
+var stateColors = map[BranchState]lipgloss.TerminalColor{
+	StateNew:    shared.ColorBlue,
+	StateOpen:   shared.ColorGreen,
+	StateDraft:  shared.ColorGray,
+	StateQueued: shared.ColorYellow,
+	StateMerged: shared.ColorPurple,
+	StateClosed: shared.ColorRed,
 }
 
-// State background tints for pill badges (dark 256-color shades that read as a
-// low-opacity wash of the foreground color across most terminal themes).
-var stateBgColors = map[BranchState]lipgloss.Color{
-	StateNew:    lipgloss.Color("18"),  // dark blue
-	StateOpen:   lipgloss.Color("22"),  // dark green
-	StateDraft:  lipgloss.Color("238"), // dark gray
-	StateQueued: lipgloss.Color("58"),  // dark brown
-	StateMerged: lipgloss.Color("53"),  // dark purple
-	StateClosed: lipgloss.Color("52"),  // dark red
+// State background tints for pill badges: dark washes on a dark terminal, light
+// washes on a light terminal, so the badge reads as a low-opacity tint of its
+// foreground color in either mode.
+var stateBgColors = map[BranchState]lipgloss.TerminalColor{
+	StateNew:    lipgloss.AdaptiveColor{Dark: "#10243e", Light: "#cfe7ff"},
+	StateOpen:   lipgloss.AdaptiveColor{Dark: "#0d2818", Light: "#c8f0d4"},
+	StateDraft:  lipgloss.AdaptiveColor{Dark: "#272b33", Light: "#e4e9ef"},
+	StateQueued: lipgloss.AdaptiveColor{Dark: "#2b2410", Light: "#f4ead9"},
+	StateMerged: lipgloss.AdaptiveColor{Dark: "#241a3a", Light: "#ecdcff"},
+	StateClosed: lipgloss.AdaptiveColor{Dark: "#2d1417", Light: "#ffdcd7"},
 }
 
 // Label returns the uppercase badge text for a state (e.g. "NEW").
@@ -44,7 +50,7 @@ func (s BranchState) Label() string {
 }
 
 // Color returns the foreground color associated with a state.
-func (s BranchState) Color() lipgloss.Color { return stateColors[s] }
+func (s BranchState) Color() lipgloss.TerminalColor { return stateColors[s] }
 
 // Dot returns the compact status glyph for a state.
 func (s BranchState) Dot() string {
@@ -84,86 +90,83 @@ func RenderDot(s BranchState) string {
 
 // Shared submit-view styles. These are intentionally centralized so the left
 // stack tree, the editor, and the chrome render with a consistent visual
-// language.
+// language. Colors come from the background-aware palette in internal/tui/shared.
 var (
-	focusNameStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("14")).Bold(true) // cyan focused label
+	focusNameStyle = lipgloss.NewStyle().Foreground(shared.ColorAccent).Bold(true) // focused label
 	// headerBranchStyle renders the focused branch name in the right-panel card
-	// header in white (the left-panel cursor name stays cyan).
-	headerBranchStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true)
+	// header in primary ink (the left-panel cursor name uses the accent color).
+	headerBranchStyle = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true)
 
 	// rowShadeColor tints the focused (currently-viewed) branch row in the left
-	// timeline. A neutral cool gray (truecolor, so it doesn't pick up a warm tint
-	// from a themed 256-color palette) reading as a translucent-white highlight.
-	rowShadeColor = lipgloss.Color("#3b3e46")
+	// timeline, reading as a subtle highlight on either background.
+	rowShadeColor = shared.ColorRowShade
 
 	// Panel border shared by both panels (focus is shown on the active input
 	// field, not the panel frame).
 	panelBorderStyle = lipgloss.NewStyle().
 				Border(lipgloss.RoundedBorder()).
-				BorderForeground(lipgloss.Color("8")).
+				BorderForeground(shared.ColorBorder).
 				Padding(0, 1)
 
 	// Section labels (e.g. STACK, EDITING, TITLE, DESCRIPTION).
-	sectionLabelStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8")).Bold(true)
+	sectionLabelStyle = lipgloss.NewStyle().Foreground(shared.ColorTextMuted).Bold(true)
 
 	// Tab strip styles.
-	tabActiveStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true).Underline(true)
-	tabInactiveStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	tabActiveStyle   = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true).Underline(true)
+	tabInactiveStyle = lipgloss.NewStyle().Foreground(shared.ColorTextMuted)
 
 	// Footer / status styles.
-	footerKeyStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("14"))
+	footerKeyStyle = lipgloss.NewStyle().Foreground(shared.ColorAccent)
 
-	// openLinkStyle renders the underlined white "↗ Open on GitHub" link (arrow
+	// openLinkStyle renders the underlined "↗ Open on GitHub" link (arrow
 	// included) in a locked PR's read-only card header; lockedTitleStyle renders
 	// that PR's title.
-	openLinkStyle    = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true).Underline(true)
-	lockedTitleStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true)
-
-	// Footer bottom-right actions: nextBranchStyle is the white "NEXT BRANCH"
-	// label; submitButtonStyle is the prominent solid-white "SUBMIT N PRs" button
-	// (dark text) shown on the last PR.
-	nextBranchStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Bold(true)
-	submitButtonStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("0")).Background(lipgloss.Color("15")).Bold(true).Padding(0, 1)
-	// prNumberStyle renders a clickable existing-PR number as an underlined
-	// white link.
-	prNumberStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("15")).Underline(true)
+	openLinkStyle    = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true).Underline(true)
+	lockedTitleStyle = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true)
+
+	// Footer bottom-right actions: nextBranchStyle is the "NEXT BRANCH" label;
+	// submitButtonStyle is the prominent inverted "SUBMIT N PRs" button shown on
+	// the last PR.
+	nextBranchStyle   = lipgloss.NewStyle().Foreground(shared.ColorText).Bold(true)
+	submitButtonStyle = lipgloss.NewStyle().Foreground(shared.ColorButtonFg).Background(shared.ColorButtonBg).Bold(true).Padding(0, 1)
+	// prNumberStyle renders a clickable existing-PR number as an underlined link.
+	prNumberStyle = lipgloss.NewStyle().Foreground(shared.ColorText).Underline(true)
 
 	// Tree spine + horizontal rules (dim chrome).
-	spineStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	ruleStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	spineStyle = lipgloss.NewStyle().Foreground(shared.ColorBorder)
+	ruleStyle  = lipgloss.NewStyle().Foreground(shared.ColorBorder)
 
 	// CREATE PR switch in the right-panel header. On: a green pill (matching the
-	// CREATE AS selected color) with a black square knob inset on the right. Off:
-	// the colors invert to a light-gray pill with a darker square inset on the
-	// left. The "CREATE PR" label uses the shared section-heading style.
-	switchOnStyle  = lipgloss.NewStyle().Background(lipgloss.Color("2"))
-	switchOffStyle = lipgloss.NewStyle().Background(lipgloss.Color("245"))
-	switchOnKnob   = lipgloss.Color("0")   // black knob (matches CREATE AS selected text)
-	switchOffKnob  = lipgloss.Color("236") // dark square on a lighter track
+	// CREATE AS selected color) with the knob inset on the right. Off: a muted
+	// track with a darker knob inset on the left.
+	switchOnStyle  = lipgloss.NewStyle().Background(shared.ColorGreen)
+	switchOffStyle = lipgloss.NewStyle().Background(lipgloss.AdaptiveColor{Dark: "#6e7681", Light: "#afb8c1"})
+	switchOnKnob   = shared.ColorOnFill // contrasts with the green track
+	switchOffKnob  = lipgloss.AdaptiveColor{Dark: "#1c2128", Light: "#57606a"}
 
 	// Segmented Ready/Draft control: the selected segment is filled green; the
-	// other is dim. Brackets/divider are dim chrome.
+	// other is muted. Brackets/divider are dim chrome.
 	segOnStyle = lipgloss.NewStyle().
-			Foreground(lipgloss.Color("0")).
-			Background(lipgloss.Color("2")).
+			Foreground(shared.ColorOnFill).
+			Background(shared.ColorGreen).
 			Bold(true).
 			Padding(0, 1)
-	segOffStyle   = lipgloss.NewStyle().Foreground(lipgloss.Color("8")).Padding(0, 1)
-	segFrameStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	segOffStyle   = lipgloss.NewStyle().Foreground(shared.ColorTextMuted).Padding(0, 1)
+	segFrameStyle = lipgloss.NewStyle().Foreground(shared.ColorBorder)
 
 	// dimBodyStyle renders the skipped branch's body as muted, non-interactive
 	// chrome.
-	dimBodyStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("240"))
+	dimBodyStyle = lipgloss.NewStyle().Foreground(shared.ColorTextFaint)
 
 	// descCursorStyle renders the block cursor overlaid on the scrollable
 	// description view.
 	descCursorStyle = lipgloss.NewStyle().Reverse(true)
 
 	// Description scrollbar (track + thumb), drawn inside the box.
-	scrollTrackStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	scrollThumbStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("15"))
+	scrollTrackStyle = lipgloss.NewStyle().Foreground(shared.ColorBorder)
+	scrollThumbStyle = lipgloss.NewStyle().Foreground(shared.ColorText)
 
 	// Callouts.
-	calloutErrorStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("1"))
-	hintStyle         = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	calloutErrorStyle = lipgloss.NewStyle().Foreground(shared.ColorRed)
+	hintStyle         = lipgloss.NewStyle().Foreground(shared.ColorTextMuted)
 )