Thinking/reasoning text is unreadable on dark backgrounds (hardcoded dim color) #3866

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1. github-actions

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   triage

   on Jun 19, 2026
2. examon

   added

   area:theming-accessibilityVisual themes, colors, dark/light mode, contrast, screen readers, i18n/RTLVisual themes, colors, dark/light mode, contrast, screen readers, i18n/RTL

   on Jun 19, 2026
3. examon

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   Bug

   issue type on Jun 19, 2026
4. github-actions

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   triage

   on Jun 19, 2026
5. X1aomu commented on Jun 23, 2026

   

   X1aomu

   on Jun 23, 2026

   Last edited by X1aomu

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   Debugging

   I did some deep diving with strace and found out that this issue is highly relevant to OSC 4.

   Here is my test matrix:

   ✅ Working properly:

   • Arch Linux + Kitty + tmux (3.6b)
   • WSL + Windows Terminal (without tmux)

   ❌ Reproduces the issue (Bad):

   • WSL + Windows Terminal + tmux (3.5a) — Completely no OSC 4 forwarding.
   • WSL + Windows Terminal + tmux (3.6a/3.6b) — OSC 4 is forwarded, but the sequence is broken. The OSC 4 response is out of order and incomplete.
   • WSL + Alacritty + tmux (3.6a/3.6b) — (Not fully analyzed yet. I included this as a control group to rule out Windows Terminal specific issues).

   Conclusion:
   Based on these tests, the problem seems to be related to how tmux interacts with certain components in WSL/Windows (possibly ConPTY). At this moment, it's hard to say definitively whether the root cause lies within tmux or Windows.

   Unfortunately, I don't have the time to do further debugging on this right now, but I hope these findings help point in the right direction!

   ---

   Additional Note & Suggestion for Copilot CLI

   My suggestion for the copilot-cli would be to avoid relying strictly on OSC 4. Simply querying the default foreground/background color is usually enough to infer whether the terminal is using a light or dark theme, which would allow the CLI to apply an appropriate color scheme.

   For comparison, both codex-cli and claude-code are able to render colors perfectly fine even when OSC 4 is unavailable. Their auto modes can successfully detect the terminal's light/dark mode and apply the correct configuration automatically. Falling back to a similar approach in copilot-cli would make it much more robust across different terminal environments.

   ---

   Current Workaround

   You can explicitly configure pane-colours in your tmux config. This prevents tmux from forwarding OSC 4 to the outer terminal and instead returns the values directly to the app. I've verified this works.

   Honestly, I‘m really not for this workaround, because it”s not KISS(repeating the palette from terminal to tmux). Just in any case you really want to make copilot-cli happy :)

   Here is the example tmux conf:

   setw -g pane-colours[0]  "#1e2124"
   setw -g pane-colours[1]  "#ff6e5e"
   setw -g pane-colours[2]  "#5eff6c"
   setw -g pane-colours[3]  "#ffbd5e"
   setw -g pane-colours[4]  "#5ea1ff"
   setw -g pane-colours[5]  "#bd5eff"
   setw -g pane-colours[6]  "#5ef1ff"
   setw -g pane-colours[7]  "#acacac"
   setw -g pane-colours[8]  "#7b8496"
   setw -g pane-colours[9]  "#ff5ea0"
   setw -g pane-colours[10] "#15ff00"
   setw -g pane-colours[11] "#f1ff5e"
   setw -g pane-colours[12] "#0095ff"
   setw -g pane-colours[13] "#ff5ef1"
   setw -g pane-colours[14] "#00ffea"
   setw -g pane-colours[15] "#ffffff"
   
6. copilot-cli-bot commented on Oct 10, 2026

   

   copilot-cli-botBot

   on Oct 10, 2026

   More actions

   This appears to be resolved as of GitHub Copilot CLI v1.0.95. Please update to that release or a newer stable version. We're closing this as completed. If it still happens, please comment with your version and reproduction steps.
7. copilot-cli-bot

   closed this as completedon Oct 10, 2026