fix(theme): update default theme colors for improved contrast

[clocky]

Summary

Updates both light and dark theme colors to ensure a minimum 4.5:1 contrast ratio in xterm-256 environments, specifically targeting improved visibility and accessibility for macOS Terminal.app.

Details

• Adjusted darkTheme colors to meet 4.5:1 contrast standards against the default black background.
• Adjusted lightTheme colors to meet 4.5:1 contrast standards against the default white/light-gray background.
• Scope: This PR only targets the default darkTheme and lightTheme definitions; no other themes (e.g., Ayu, GitHub, Solarized) are affected.

Related Issues

Fixes #21170

[gemini-cli]

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[gemini-cli]

Hi @clocky, thank you so much for your contribution to Gemini CLI! We really appreciate the time and effort you've put into this.

We're making some updates to our contribution process to improve how we track and review changes. Please take a moment to review our recent discussion post: Improving Our Contribution Process & Introducing New Guidelines.

Key Update: Starting January 26, 2026, the Gemini CLI project will require all pull requests to be associated with an existing issue. Any pull requests not linked to an issue by that date will be automatically closed.

Thank you for your understanding and for being a part of our community!

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the accessibility and legibility of the CLI's themes by adjusting color palettes for both light and dark modes. The changes are specifically designed to meet contrast ratio standards in xterm-256 compatible terminal emulators, particularly macOS Terminal.app, ensuring a more comfortable and compliant user experience. A new utility script has also been added to facilitate the validation and preview of these color changes.

Highlights

• Improved Theme Contrast: Updated both light and dark theme colors to ensure a minimum 4.5:1 contrast ratio, specifically targeting improved visibility and accessibility in xterm-256 environments like macOS Terminal.app.
• New Theme Preview Script: Introduced a new script to preview theme colors, calculate their contrast ratios, and display their closest xterm-256 approximations, aiding in visual verification and accessibility compliance.

Changelog

• packages/cli/src/ui/themes/theme.ts
  • Updated color definitions for lightTheme to improve contrast and simplify color assignments.
  • Updated color definitions for darkTheme to improve contrast and simplify color assignments.
  • Removed interpolateColor function calls for direct hex color assignments.
• scripts/preview-dark-theme.ts
  • Added a new script to preview theme colors and their contrast ratios.
  • Implemented logic to find the closest xterm-256 color approximation for given hex values.
  • Included functions to rate contrast levels (AAA, AA, LG, FAIL) for better accessibility insights.

Activity

• The author has validated the changes on MacOS using 'npm run'.

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[clocky]

Fixes #21170

[gemini-code-assist]

Code Review

This pull request significantly improves the accessibility and contrast of the default light and dark themes by updating their color definitions to meet a minimum 4.5:1 contrast ratio, especially for xterm-256 environments like macOS Terminal.app. A new script scripts/preview-dark-theme.ts has been added to aid in validating these color changes. However, there's a critical inconsistency in how these colors are handled, which might undermine the PR's primary goal.