diff --git a/ui-tui/src/__tests__/theme.test.ts b/ui-tui/src/__tests__/theme.test.ts
index fb7f7867025a..5496ae6117d0 100644
--- a/ui-tui/src/__tests__/theme.test.ts
+++ b/ui-tui/src/__tests__/theme.test.ts
@@ -653,3 +653,31 @@ describe('background-aware adaptation (OSC-11 light terminals)', () => {
     expect(color.statusCritical).toBe(fromSkin({ ui_error: '#dd2222' }, {}).color.error)
   })
 })
+
+describe('themeToneHex', () => {
+  it('resolves a tone to the literal color it paints as', async () => {
+    const { themeToneHex } = await importThemeWithCleanEnv()
+
+    // 232+ is the grayscale ramp (8 + (n-232)*10); 16-231 is the 6x6x6 cube.
+    expect(themeToneHex('ansi256(238)')).toBe('#444444')
+    expect(themeToneHex('ansi256(161)')).toBe('#d7005f')
+    // An authored hex is already literal.
+    expect(themeToneHex('#e77fa3')).toBe('#e77fa3')
+    // No paintable color ⇒ '', which releases the terminal default.
+    expect(themeToneHex('')).toBe('')
+    expect(themeToneHex('ansi256(999)')).toBe('')
+    expect(themeToneHex('inherit')).toBe('')
+  })
+
+  it('makes every tone paintable on a quantizing terminal', async () => {
+    // The contract OSC-10 depends on: whatever the palette normalizer does to
+    // a tone, themeToneHex still yields a literal `#rrggbb`. Asserted over the
+    // whole palette so a new tone can't silently regress the default paint.
+    const { fromSkin, themeToneHex } = await importThemeWithEnv({ TERM_PROGRAM: 'Apple_Terminal' })
+    const { color } = fromSkin({ background: '#f6f9fd', ui_text: '#4a4550' }, {})
+
+    for (const tone of Object.values(color)) {
+      expect(themeToneHex(tone)).toMatch(/^#[0-9a-f]{6}$/i)
+    }
+  })
+})
diff --git a/ui-tui/src/app/createGatewayEventHandler.ts b/ui-tui/src/app/createGatewayEventHandler.ts
index d8630e216736..bbd826138607 100644
--- a/ui-tui/src/app/createGatewayEventHandler.ts
+++ b/ui-tui/src/app/createGatewayEventHandler.ts
@@ -22,7 +22,7 @@ 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, fromSkin, skinIsLight, type Theme } from '../theme.js'
+import { defaultThemeForCurrentBackground, fromSkin, skinIsLight, type Theme, themeToneHex } from '../theme.js'
 import type { Msg, SubagentProgress, SubagentStatus } from '../types.js'
 
 import { applyDelegationStatus, getDelegationState } from './delegationStore.js'
@@ -126,11 +126,13 @@ const themesEqual = (a: Theme, b: Theme) => {
 // the theme's text color. Without the pair, a dark skin on a light terminal
 // leaves default-fg text at the HOST's near-black: invisible. Opt-in stays
 // intact: no `background` ⇒ both defaults restore to the terminal's own.
+// The text tone resolves through themeToneHex because a limited-palette
+// terminal quantizes it to `ansi256(N)`, which OSC-10 cannot speak.
 const paintTerminalDefaults = (theme: Theme) => {
   const background = lastSkin?.colors?.background ?? ''
 
   setTerminalBackground(background)
-  setTerminalForeground(isPaintableHex(background) ? theme.color.text : '')
+  setTerminalForeground(isPaintableHex(background) ? themeToneHex(theme.color.text) : '')
 }
 
 const applySkin = (s: GatewaySkin) => {
diff --git a/ui-tui/src/theme.ts b/ui-tui/src/theme.ts
index 7ddd75a4e61d..11ef94131567 100644
--- a/ui-tui/src/theme.ts
+++ b/ui-tui/src/theme.ts
@@ -222,6 +222,31 @@ function normalizeAnsiForeground(color: string): string {
   return `ansi256(${ansi})`
 }
 
+const ANSI256_RE = /^ansi256\((\d{1,3})\)$/
+
+/**
+ * The literal `#rrggbb` a theme tone paints as, or '' when it has none.
+ *
+ * The inverse of `normalizeAnsiForeground`: tones are not uniformly hex, since
+ * a limited-palette terminal rewrites the foregrounds to `ansi256(N)`.
+ * Consumers needing a real color — OSC 10/11, which only speak `#rrggbb` —
+ * resolve through here rather than hex-testing the tone, which would silently
+ * skip exactly the terminals that did the quantizing.
+ */
+export function themeToneHex(tone: string): string {
+  const ansi = ANSI256_RE.exec(tone.trim())
+
+  if (ansi) {
+    const n = Number(ansi[1])
+
+    return n <= 255 ? toHex(xtermEightBitRgb(n)) : ''
+  }
+
+  const rgb = parseColor(tone)
+
+  return rgb ? toHex(rgb) : ''
+}
+
 // ── Defaults ─────────────────────────────────────────────────────────
 
 const BRAND: ThemeBrand = {