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tty.WriteStream.getColorDepth() returns 8 inside tmux despite COLORTERM=truecolor #62404
Description
Bug
In lib/internal/tty.js, getColorDepth() checks env.TMUX (line 174) before env.COLORTERM (line 215). When TMUX is set, it returns COLORS_256 (8) immediately, never reaching the COLORTERM === 'truecolor' check that would return COLORS_16m (24).
tmux has supported true color since v2.2 (2016). Modern tmux sets COLORTERM=truecolor when the outer terminal supports RGB via terminal-features or terminal-overrides. The current ordering ignores this.
Note: PR #30474 previously reordered COLORTERM before the TERM check but did not address the TMUX check ordering.
Reproduction
const tty = require('tty');
console.log('TMUX:', process.env.TMUX || '(unset)');
console.log('COLORTERM:', process.env.COLORTERM || '(unset)');
console.log('getColorDepth():', process.stdout.getColorDepth());Inside tmux (with COLORTERM=truecolor):
TMUX: /private/tmp/tmux-501/default,9842,1
COLORTERM: truecolor
getColorDepth(): 8 # ← wrong, should be 24
With TMUX= unset:
TMUX: (unset)
COLORTERM: truecolor
getColorDepth(): 24 # ← correct
Suggested fix
Move the COLORTERM truecolor/24bit check (line 215) before the TMUX check (line 174):
// Check COLORTERM first — tmux sets this when RGB is supported
if (env.COLORTERM === 'truecolor' || env.COLORTERM === '24bit') {
return COLORS_16m;
}
if (env.TMUX) {
return COLORS_256;
}This preserves the TMUX → 256 fallback for tmux sessions that don't have truecolor configured, while correctly returning 16m for those that do.
Related
- PR tty: truecolor check moved before 256 check #30474 — moved truecolor check before
TERM256 check (but not beforeTMUX) - Bun has the same bug (filed at
getColorDepth()returns 8 (256-color) inside tmux despite COLORTERM=truecolor oven-sh/bun#28463), inherited from this code
Activity
semimikoh commentedon Mar 24, 2026
Thanks for the detailed bug report! I'd like to work on fixing this issue.
My plan:
Is it okay if I submit a PR for this?
jacobcxdev commentedon Mar 24, 2026
@semimikoh yeah that's fine by me—thanks for taking it on!
github-actions commentedon Jul 20, 2026
This issue has been marked as stale due to 90 days of inactivity.
It will be automatically closed in 30 days if no further activity occurs. If this is still relevant, please leave a comment or update it to keep it open.
jacobcxdev commentedon Jul 20, 2026
I believe this may still be relevant.
semimikoh commentedon Jul 21, 2026
Following up on this — I looked into it, and it turns out this has already been fixed on
mainand released.In PR #58146 (
tty: improve color terminal color detection), theenv.TMUXbranch inlib/internal/tty.jswas changed to returnCOLORS_16m(24) instead ofCOLORS_256(8):So
getColorDepth()now returns24inside tmux. This shipped in v25.0.0, and there's already a regression test covering it intest/pseudo-tty/test-tty-color-support.js:@jacobcxdev could you confirm which Node version you're on? If you're on v24 or earlier, upgrading to v25.0.0+ should resolve this. Given it's already fixed on
main, I think this issue can be closed.