Light theme user-message background hardcoded to #eeeeee, clashes with non-white terminal backgrounds

Problem

In light mode, the user-message block renders with a hardcoded #eeeeee background. The color is emitted directly as a 24-bit RGB value, not mapped to an ANSI palette slot, so it overrides whatever the terminal's theme provides.

Why this is a problem

Any terminal set up with a light theme that isn't pure white gets a visible grey stripe around user messages that doesn't match the rest of the UI chrome. Because #eeeeee is hardcoded, there's no way to make it pair correctly from outside Claude Code.

Concrete example

• Terminal: Ghostty
• Terminal background: #f3e9d7 (Pantone Sand Dollar-ish cream, tuned for outdoor use)
• Claude Code: "theme": "light" in ~/.claude.json, v2.1.114

The user-message block shows up as a flat #eeeeee band over cream. Verified by sampling the PNG pixel values — consistently #eeeeee inside the band, ~#f3e9d7 outside.

Suggested fixes (any one of these would help)

1. Don't set a background color for the user-message block — let the terminal's default bg show through. Simplest fix, respects every terminal theme automatically.
2. Derive the message bg from the user's configured theme (e.g. slightly lighter/darker than the terminal's default, computed at runtime).
3. Use an ANSI palette slot (e.g. one of the 16 ANSI slots or the 256-color range) rather than 24-bit truecolor, so terminal themes can re-map it.
4. Expose a settings key (userMessageBackground or similar) so users can set it per-machine.

Option 1 is the lowest-effort and probably gets the best result for the largest number of terminal themes.

Environment

• Claude Code: 2.1.114
• OS: macOS 14 (Darwin 24.6.0, arm64)
• Terminal: Ghostty (latest)
• Claude theme: light