diff --git a/ui-tui/src/__tests__/theme.test.ts b/ui-tui/src/__tests__/theme.test.ts
index ad54c285fa64..fb7f7867025a 100644
--- a/ui-tui/src/__tests__/theme.test.ts
+++ b/ui-tui/src/__tests__/theme.test.ts
@@ -302,6 +302,42 @@ describe('fromSkin', () => {
     expect(theme.color.prompt).toBe('ansi256(136)')
   })
 
+  // ── A skin that authors a background OWNS its polarity ──────────────
+  // The TUI paints the terminal with the skin's background (OSC-11), so
+  // every adaptation pass must run against the skin's canvas, not the host
+  // profile the skin just covered. The real-world failure: a pure-black
+  // skin on light-mode Apple Terminal got its text ansi256-bucketed for a
+  // light background that no longer exists — invisible on the painted black.
+
+  it('a dark-background skin on light Apple Terminal keeps its truecolor text (no light-mode bucketing)', async () => {
+    const { fromSkin } = await importThemeWithEnv({ TERM_PROGRAM: 'Apple_Terminal' })
+
+    const theme = fromSkin({ background: '#000000', ui_accent: '#ff9e18', ui_text: '#ffa726' }, {})
+
+    expect(theme.color.text).toBe('#ffa726')
+    expect(theme.color.prompt).not.toMatch(/^ansi256/)
+  })
+
+  it('a skin background outranks the cached host background for adaptation and tone derivation', async () => {
+    const { fromSkin } = await importThemeWithEnv({ HERMES_TUI_BACKGROUND: '#ffffff' })
+
+    const theme = fromSkin({ background: '#000000', ui_text: '#ffa726' }, {})
+
+    // Text is not contrast-lifted toward a white host it painted over…
+    expect(theme.color.text).toBe('#ffa726')
+    // …and derived fills mix against the skin's black, not the host's white.
+    expect(luminance(theme.color.completionBg)).toBeLessThanOrEqual(0.35)
+    expect(luminance(theme.color.statusBg)).toBeLessThanOrEqual(0.35)
+  })
+
+  it('skinIsLight: the authored background decides; host detection only when absent', async () => {
+    const { skinIsLight } = await importThemeWithEnv({ HERMES_TUI_BACKGROUND: '#ffffff' })
+
+    expect(skinIsLight({ background: '#000000' })).toBe(false)
+    expect(skinIsLight({ background: '#f5f5f5' })).toBe(true)
+    expect(skinIsLight({})).toBe(true) // no canvas of its own → host polarity
+  })
+
   it('keeps truecolor light Apple Terminal in truecolor (adapting, not ansi256-bucketing)', async () => {
     const { contrastRatio, fromSkin } = await importThemeWithEnv({
       COLORTERM: 'truecolor',
diff --git a/ui-tui/src/app/createGatewayEventHandler.ts b/ui-tui/src/app/createGatewayEventHandler.ts
index ec0fb02748ba..fccb499b0e4e 100644
--- a/ui-tui/src/app/createGatewayEventHandler.ts
+++ b/ui-tui/src/app/createGatewayEventHandler.ts
@@ -21,7 +21,7 @@ import { topLevelSubagents } from '../lib/subagentTree.js'
 import { isPaintableHex, setTerminalBackground, setTerminalForeground } from '../lib/terminalModes.js'
 import { formatAbandonedClarify, formatToolCall, stripAnsi } from '../lib/text.js'
 import { bootSeededPin, invalidateBootBackground, writeBootTheme } from '../lib/themeBoot.js'
-import { defaultThemeForCurrentBackground, detectLightMode, fromSkin, type Theme } from '../theme.js'
+import { defaultThemeForCurrentBackground, fromSkin, skinIsLight, type Theme } from '../theme.js'
 import type { Msg, SubagentProgress, SubagentStatus } from '../types.js'
 
 import { applyDelegationStatus, getDelegationState } from './delegationStore.js'
@@ -45,8 +45,10 @@ const themeForSkin = (s: GatewaySkin) => {
   // can ship a fills-only `light_colors` (flip the dark navy menu/status fills
   // to light on a light terminal) while its vivid foreground golds keep coming
   // from `colors` and render raw through fromSkin's shim. A full paired block
-  // still works — it just overrides every key it lists.
-  const paired = detectLightMode() ? s.light_colors : s.dark_colors
+  // still works — it just overrides every key it lists. Polarity follows the
+  // skin's authored background when it has one (the skin paints the terminal
+  // with it), else the host's.
+  const paired = skinIsLight(s.colors ?? {}) ? s.light_colors : s.dark_colors
 
   const colors = paired && Object.keys(paired).length ? { ...(s.colors ?? {}), ...paired } : (s.colors ?? {})
 
diff --git a/ui-tui/src/theme.ts b/ui-tui/src/theme.ts
index bfd777a2f0c3..7ddd75a4e61d 100644
--- a/ui-tui/src/theme.ts
+++ b/ui-tui/src/theme.ts
@@ -788,6 +788,28 @@ export function defaultThemeForCurrentBackground(env: NodeJS.ProcessEnv = proces
 
 // ── Skin → Theme ─────────────────────────────────────────────────────
 
+/** The skin's authored canvas as a #-prefixed hex, or null when absent/junk. */
+const authoredBackground = (raw: string | undefined): null | string => {
+  const v = (raw ?? '').trim()
+
+  return backgroundLuminance(v) === null ? null : v.startsWith('#') ? v : `#${v}`
+}
+
+/**
+ * A skin that authors a background OWNS its polarity: the TUI paints the
+ * terminal with it (applySkin → OSC-11), so contrast adaptation, the derived
+ * tone ladder, and ANSI light-terminal normalization must all run against the
+ * skin's canvas — not the host profile the skin just covered. (A pure-black
+ * skin on a light Apple Terminal otherwise gets its text remapped for a light
+ * background it painted over: invisible.) Host detection still governs skins
+ * without a background — they render on the terminal's own surface.
+ */
+export function skinIsLight(colors: SkinColors, env: NodeJS.ProcessEnv = process.env): boolean {
+  const authored = backgroundLuminance(colors['background'] ?? '')
+
+  return authored === null ? detectLightMode(env) : authored >= LUMA_LIGHT_THRESHOLD
+}
+
 export function fromSkin(
   colors: SkinColors,
   branding: SkinBranding,
@@ -796,11 +818,13 @@ export function fromSkin(
   toolPrefix = '',
   helpHeader = ''
 ): Theme {
-  // Live detection (not the module-load snapshot): by the time the gateway
-  // skin arrives, the OSC-11 background probe has usually answered and cached
-  // itself into HERMES_TUI_BACKGROUND. See #applySkin / syncThemeToTerminalBackground.
-  const isLight = detectLightMode()
-  const bg = referenceBackground(isLight)
+  // Polarity: the skin's own canvas when it authors one (see skinIsLight);
+  // otherwise live host detection (not the module-load snapshot — by the time
+  // the gateway skin arrives, the OSC-11 probe has usually answered and cached
+  // itself into HERMES_TUI_BACKGROUND. See #applySkin / syncThemeToTerminalBackground).
+  const skinBg = authoredBackground(colors['background'])
+  const isLight = skinIsLight(colors)
+  const bg = skinBg ?? referenceBackground(isLight)
   const base = isLight ? LIGHT_SEEDS : DARK_SEEDS
   const d = isLight ? LIGHT_THEME : DARK_THEME
   const c = (k: string) => colors[k]