[BUG] Logo and "Thinking" animation colors are dull/washed-out inside tmux

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 running Claude Code inside tmux, the logo and "Thinking" animation text appear dull/washed-out compared to running Claude Code directly in the terminal. All other colors in tmux work correctly, and Claude Code's own text output (syntax highlighting, markdown, etc.) appears fine - only the branding UI elements (logo, thinking animation) are affected.

What Should Happen?

Logo and "Thinking" animation should have the same vibrant colors inside tmux as when running directly in the terminal.

Error Messages/Logs

Steps to Reproduce

1. Open iTerm2
2. Run claude - observe vibrant logo colors
3. Open tmux inside iTerm2
4. Run claude - observe dull/muted logo and "Thinking" animation colors

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.77 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Environment

• Claude Code version: 2.1.77
• OS: macOS (Darwin 25.3.0, Apple Silicon)
• Terminal: iTerm2
• tmux version: 3.6
• Shell: zsh
• Theme: dark

tmux config (relevant parts):
set -g default-terminal "tmux-256color"
set -ag terminal-overrides ",xterm-256color:Tc"
set -g mouse on
set -s extended-keys on
set -as terminal-features ',xterm-256color:extkeys'

What I've tried (none of these fixed the issue):

• Setting COLORTERM=truecolor via set-environment -g COLORTERM truecolor
• Setting FORCE_COLOR=3 environment variable
• Adding set -ag terminal-overrides ",tmux-256color:RGB"
• Setting set -g allow-passthrough all
• Setting set-environment -g TERM_PROGRAM iTerm.app
• Setting COLORFGBG="15;0" in shell
• Changing default-terminal to xterm-256color
• Setting theme to dark via /theme

Truecolor verification:
Truecolor works correctly inside tmux for all other applications. Running the following produces three distinct, vibrant orange blocks:

printf '\e[38;2;231;111;44m██████ truecolor\e[0m\n'
printf '\e[38;5;208m██████ 256-color\e[0m\n'
printf '\e[38;2;204;102;0m██████ truecolor darker\e[0m\n'

Suspected cause
Claude Code likely performs its own terminal capability detection for UI elements and falls back to a muted color palette when it detects tmux, regardless of actual truecolor support.