[BUG] Background colors more muted since 2.1.77 tmux "fix"

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When I upgraded from Claude Code 2.1.76 to 2.1.77, I immediately noticed colors appear duller/washed out.
I think this is linked to "Fixed background colors rendering as terminal-default inside tmux" in the release notes: sounds like it fixed an issue for some users but broke it for others like me who already had set it up correctly.
I have:

• Terminal: Ghostty
• Multiplexer: tmux
• COLORTERM=truecolor
• default-terminal: tmux-256color
• terminal-overrides: xterm-ghostty:RGB, xterm-256color:RGB

My tmux config already had truecolor working correctly before the "fix". So the fix seems to have introduced a regression.

What Should Happen?

truecolor working

Error Messages/Logs

Steps to Reproduce

open Claude Code after upgrading to 2.1.77 and notice muted colors.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.76

Claude Code Version

2.1.77

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

_No response_