diff --git a/packages/cli/src/ui/themes/theme.ts b/packages/cli/src/ui/themes/theme.ts
index 7785e9bda06..da7bccf1b20 100644
--- a/packages/cli/src/ui/themes/theme.ts
+++ b/packages/cli/src/ui/themes/theme.ts
@@ -185,69 +185,45 @@ export interface ColorsTheme {
 
 export const lightTheme: ColorsTheme = {
   type: 'light',
-  Background: '#FAFAFA',
-  Foreground: '',
-  LightBlue: '#89BDCD',
-  AccentBlue: '#3B82F6',
-  AccentPurple: '#8B5CF6',
-  AccentCyan: '#06B6D4',
-  AccentGreen: '#3CA84B',
-  AccentYellow: '#D5A40A',
-  AccentRed: '#DD4C4C',
-  DiffAdded: '#C6EAD8',
-  DiffRemoved: '#FFCCCC',
-  Comment: '#008000',
-  Gray: '#97a0b0',
-  DarkGray: interpolateColor('#FAFAFA', '#97a0b0', DEFAULT_BORDER_OPACITY),
-  InputBackground: interpolateColor(
-    '#FAFAFA',
-    '#97a0b0',
-    DEFAULT_INPUT_BACKGROUND_OPACITY,
-  ),
-  MessageBackground: interpolateColor(
-    '#FAFAFA',
-    '#97a0b0',
-    DEFAULT_INPUT_BACKGROUND_OPACITY,
-  ),
-  FocusBackground: interpolateColor(
-    '#FAFAFA',
-    '#3CA84B',
-    DEFAULT_SELECTION_OPACITY,
-  ),
+  Background: '#FFFFFF',
+  Foreground: '#000000',
+  LightBlue: '#005FAF',
+  AccentBlue: '#005FAF',
+  AccentPurple: '#5F00FF',
+  AccentCyan: '#005F87',
+  AccentGreen: '#005F00',
+  AccentYellow: '#875F00',
+  AccentRed: '#AF0000',
+  DiffAdded: '#D7FFD7',
+  DiffRemoved: '#FFD7D7',
+  Comment: '#008700',
+  Gray: '#5F5F5F',
+  DarkGray: '#5F5F5F',
+  InputBackground: '#E4E4E4',
+  MessageBackground: '#FAFAFA',
+  FocusBackground: '#D7FFD7',
   GradientColors: ['#4796E4', '#847ACE', '#C3677F'],
 };
 
 export const darkTheme: ColorsTheme = {
   type: 'dark',
-  Background: '#1E1E2E',
-  Foreground: '',
-  LightBlue: '#ADD8E6',
-  AccentBlue: '#89B4FA',
-  AccentPurple: '#CBA6F7',
-  AccentCyan: '#89DCEB',
-  AccentGreen: '#A6E3A1',
-  AccentYellow: '#F9E2AF',
-  AccentRed: '#F38BA8',
-  DiffAdded: '#28350B',
-  DiffRemoved: '#430000',
-  Comment: '#6C7086',
-  Gray: '#6C7086',
-  DarkGray: interpolateColor('#1E1E2E', '#6C7086', DEFAULT_BORDER_OPACITY),
-  InputBackground: interpolateColor(
-    '#1E1E2E',
-    '#6C7086',
-    DEFAULT_INPUT_BACKGROUND_OPACITY,
-  ),
-  MessageBackground: interpolateColor(
-    '#1E1E2E',
-    '#6C7086',
-    DEFAULT_INPUT_BACKGROUND_OPACITY,
-  ),
-  FocusBackground: interpolateColor(
-    '#1E1E2E',
-    '#A6E3A1',
-    DEFAULT_SELECTION_OPACITY,
-  ),
+  Background: '#000000',
+  Foreground: '#FFFFFF',
+  LightBlue: '#AFD7D7',
+  AccentBlue: '#87AFFF',
+  AccentPurple: '#D7AFFF',
+  AccentCyan: '#87D7D7',
+  AccentGreen: '#D7FFD7',
+  AccentYellow: '#FFFFAF',
+  AccentRed: '#FF87AF',
+  DiffAdded: '#005F00',
+  DiffRemoved: '#5F0000',
+  Comment: '#AFAFAF',
+  Gray: '#AFAFAF',
+  DarkGray: '#878787',
+  InputBackground: '#5F5F5F',
+  MessageBackground: '#5F5F5F',
+  FocusBackground: '#005F00',
   GradientColors: ['#4796E4', '#847ACE', '#C3677F'],
 };
 
diff --git a/scripts/preview-dark-theme.ts b/scripts/preview-dark-theme.ts
new file mode 100644
index 00000000000..59dd4f9bbee
--- /dev/null
+++ b/scripts/preview-dark-theme.ts
@@ -0,0 +1,198 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+import chalk from 'chalk';
+import tinycolor from 'tinycolor2';
+import tinygradient from 'tinygradient';
+import {
+  darkTheme,
+  lightTheme,
+  type ColorsTheme,
+} from '../packages/cli/src/ui/themes/theme.js';
+
+const BLACK = '#000000';
+const WHITE = '#FFFFFF';
+const TABLE_WIDTH = 85;
+const backgroundColors = new Set([
+  'Background',
+  'DiffAdded',
+  'DiffRemoved',
+  'InputBackground',
+  'MessageBackground',
+  'FocusBackground',
+]);
+
+// xterm-256 levels as specified
+const CUBE_LEVELS = [0, 95, 135, 175, 215, 255];
+const GRAY_LEVELS = Array.from({ length: 24 }, (_, i) => 8 + i * 10);
+
+function toHex(n: number) {
+  return n.toString(16).padStart(2, '0');
+}
+
+function getClosestXterm(hex: string): { code: number; hex: string } {
+  if (!hex || hex === '') return { code: 0, hex: '#000000' };
+  const color = tinycolor(hex).toRgb();
+
+  // 1. Check Grayscale ramp (232-255)
+  let bestGray = -1;
+  let minGrayDist = Infinity;
+  // Simple grayscale conversion
+  const avg = (color.r + color.g + color.b) / 3;
+  for (let i = 0; i < GRAY_LEVELS.length; i++) {
+    const dist = Math.abs(GRAY_LEVELS[i] - avg);
+    if (dist < minGrayDist) {
+      minGrayDist = dist;
+      bestGray = i;
+    }
+  }
+
+  // 2. Check Color Cube (16-231)
+  const findClosestLevel = (val: number) => {
+    let bestL = 0;
+    let minDist = Infinity;
+    for (let i = 0; i < CUBE_LEVELS.length; i++) {
+      const dist = Math.abs(CUBE_LEVELS[i] - val);
+      if (dist < minDist) {
+        minDist = dist;
+        bestL = i;
+      }
+    }
+    return bestL;
+  };
+
+  const rIdx = findClosestLevel(color.r);
+  const gIdx = findClosestLevel(color.g);
+  const bIdx = findClosestLevel(color.b);
+
+  const cubeDist = Math.sqrt(
+    Math.pow(CUBE_LEVELS[rIdx] - color.r, 2) +
+      Math.pow(CUBE_LEVELS[gIdx] - color.g, 2) +
+      Math.pow(CUBE_LEVELS[bIdx] - color.b, 2),
+  );
+
+  // Compare grayscale vs cube distance (cube typically wins if it's colorful)
+  // We'll also check if the input is very desaturated
+  const isDesaturated =
+    Math.max(color.r, color.g, color.b) - Math.min(color.r, color.g, color.b) <
+    10;
+
+  if (isDesaturated && minGrayDist < cubeDist) {
+    const code = 232 + bestGray;
+    const v = GRAY_LEVELS[bestGray];
+    return { code, hex: `#${toHex(v)}${toHex(v)}${toHex(v)}` };
+  } else {
+    const code = 16 + 36 * rIdx + 6 * gIdx + bIdx;
+    return {
+      code,
+      hex: `#${toHex(CUBE_LEVELS[rIdx])}${toHex(CUBE_LEVELS[gIdx])}${toHex(CUBE_LEVELS[bIdx])}`,
+    };
+  }
+}
+
+function getRating(contrast: number): string {
+  const contrastStr = `${contrast.toFixed(2)}:1`;
+  if (contrast >= 7) return chalk.green(`(AAA) ${contrastStr.padEnd(7)}`);
+  if (contrast >= 4.5) return chalk.cyan(`(AA)  ${contrastStr.padEnd(7)}`);
+  if (contrast >= 3) return chalk.yellow(`(LG)  ${contrastStr.padEnd(7)}`);
+  return chalk.red(`(FAIL) ${contrastStr.padEnd(7)}`);
+}
+
+function previewTheme(themeName: string, theme: ColorsTheme) {
+  const isDark = theme.type === 'dark';
+  const baseBackground = isDark ? BLACK : WHITE;
+  const defaultForeground = isDark ? WHITE : BLACK;
+  const foreground =
+    theme.Foreground && theme.Foreground !== ''
+      ? theme.Foreground
+      : defaultForeground;
+
+  console.log(
+    '\n' +
+      chalk.bold.underline(
+        `${themeName}: Hex vs Corrected xterm-256 Comparison`,
+      ),
+  );
+  console.log(chalk.dim('xterm cube levels: 00, 5f, 87, af, d7, ff'));
+  console.log('');
+
+  const headers = [
+    'Name'.padEnd(18),
+    'Original (Hex)'.padEnd(25),
+    'Contrast Comparison',
+  ];
+  console.log(headers.join(' | '));
+  console.log('-'.repeat(TABLE_WIDTH));
+
+  for (const [name, hexValue] of Object.entries(theme)) {
+    if (Array.isArray(hexValue) || !hexValue || name === 'type') continue;
+    const hex = hexValue as string;
+
+    // 1. Correct xterm Mapping
+    const xterm = getClosestXterm(hex);
+    const xtermFg = getClosestXterm(foreground);
+    const xtermGreen = getClosestXterm(theme.AccentGreen);
+    const xtermBaseBg = getClosestXterm(baseBackground);
+
+    // 2. Previews
+    let originalPreview: string;
+    let label: string;
+
+    if (name === 'FocusBackground') {
+      originalPreview = chalk.bgHex(hex).hex(theme.AccentGreen)(' Text ');
+      label = 'vs Green';
+    } else if (backgroundColors.has(name)) {
+      originalPreview = chalk.bgHex(hex).hex(foreground)(' Text ');
+      label = 'vs Fore';
+    } else {
+      originalPreview = chalk.bgHex(baseBackground).hex(hex)(' Text ');
+      label = isDark ? 'vs Black' : 'vs White';
+    }
+
+    // 3. Contrast Ratios
+    const xtermFgHex =
+      name === 'FocusBackground'
+        ? xtermGreen.hex
+        : backgroundColors.has(name)
+          ? xtermFg.hex
+          : xterm.hex;
+    const xtermBgHex = backgroundColors.has(name) ? xterm.hex : xtermBaseBg.hex;
+
+    const originalContrast = tinycolor.readability(
+      backgroundColors.has(name)
+        ? name === 'FocusBackground'
+          ? theme.AccentGreen
+          : foreground
+        : hex,
+      backgroundColors.has(name) ? hex : baseBackground,
+    );
+    const xtermContrast = tinycolor.readability(xtermFgHex, xtermBgHex);
+
+    const originalCol = `${hex.toUpperCase().padEnd(10)} ${originalPreview}`;
+    const contrastCol = `${getRating(originalContrast)} -> ${getRating(xtermContrast)} ${chalk.dim(label)}`;
+
+    console.log(
+      `${name.padEnd(18)} | ${originalCol.padEnd(25)} | ${contrastCol}`,
+    );
+  }
+
+  console.log('-'.repeat(TABLE_WIDTH));
+  if (theme.GradientColors && theme.GradientColors.length > 0) {
+    const NAME_COL_WIDTH = 18;
+    const SEP_WIDTH = 3; // " | "
+    const gradientWidth = TABLE_WIDTH - NAME_COL_WIDTH - SEP_WIDTH;
+    const gradient = tinygradient(theme.GradientColors);
+    const gradientStr = Array.from({ length: gradientWidth }, (_, i) => {
+      const color = gradient.rgbAt(i / (gradientWidth - 1));
+      return chalk.hex(color.toHexString())('█');
+    }).join('');
+    console.log('Gradient Test'.padEnd(NAME_COL_WIDTH) + ' | ' + gradientStr);
+    console.log('-'.repeat(TABLE_WIDTH));
+  }
+}
+
+previewTheme('Dark Theme', darkTheme);
+previewTheme('Light Theme', lightTheme);
+console.log('');