Prompt box and highlighted menu items render invisible (dark-on-dark) inside tmux

[ethangarofolo-oct]

Describe the bug

Copilot CLI's prompt input box and highlighted/selected menu list items are unreadable (dark text on dark/matching background) when run inside tmux. The same session works correctly in a plain iTerm2 tab with no tmux.

During troubleshooting, ruled out the following:

• Stale  COLORFGBG  env var — unset it, no change.
• iTerm2 automatic light/dark profile switching — disabled it, no change.
• tmux truecolor passthrough — confirmed via  tmux info  that  Tc / RGB  report  true  after adding  set -ga terminal-overrides ",xterm-256color:Tc" , and  tmux capture-pane -e  shows correct 24-bit RGB SGR codes are being preserved (not quantized), so this isn't a color-depth/passthrough issue.
•  tmux allow-passthrough on  is enabled; OSC 11 background-color queries do get a reply (confirmed manually with  printf '\033]11;?\033\' ), though the reply appears to arrive after Copilot's internal detection timeout in some tests.
• Restarting tmux server fully, restarting iTerm2 fully — no change.
• Switching Copilot's  theme  setting between  default ,  dim ,  github  — same problem persists in all of them, only inside tmux.

Affected version

GitHub Copilot CLI 1.0.73. Run 'copilot update' to check for updates.

Steps to reproduce the behavior

1. Launch iTerm2, start a tmux session, run  copilot .
2. Type in the prompt input box, or open a menu with selectable items (e.g.  /theme ).
3. Text in the prompt box / highlighted menu rows is invisible — same foreground/background color.

Expected behavior

The colors should be legible regardless of being run inside tmux or not

Additional context

No response

[ethangarofolo-oct]

In a further attempt to debug, copilot said:

Found the actual root cause. Looking at the raw capture of your typed text  asdf  in the prompt box:

\x1b[38;2;180;180;180m \x1b[39m \x1b[48;2;12;12;12m asdf

Copilot sets the foreground to light gray ( 180;180;180 ), then immediately resets it to "default" ( \x1b[39m ) before setting a near-black background and printing your typed text — relying on the terminal's native default foreground color rather than an explicit one. Everywhere else in the UI (mascot, tabs, etc.) explicitly sets colors and renders fine. Only the typed-input text in the prompt box uses this "default foreground" fallback, and in your tmux environment that default resolves to something dark/near-black — hence invisible text specifically there, and nowhere else.

This is a genuine Copilot CLI bug: it should use an explicit foreground color for typed prompt text instead of relying on the terminal's ambient default, since that default isn't reliably synced through tmux. I'll fold this precise detail into the feedback report.