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Background color query (OSC 11)
ESC ] 11 ; ? BELOSC 11 queries the terminal's default background color. The query is
ESC ] 11 ; ? ST. The response format matches OSC 10. This is the most reliable way to detect whether the user has a dark or light terminal theme — compare the background color's luminance to determine the appropriate color palette.How this is testedautomated
Query background color with
Query background color with
OSC 11 ; ? BEL, verify response matches OSC 11 ; rgb:... pattern via feedCapture.The same probe runs against headless backends (via Termless) and real terminal apps (via a daemon launched in each terminal). This lets us distinguish parser correctness from rendering correctness.
Analysis2026-04-06
Supported by 7 of 14 backends (50%)
Terminal Applications
| Terminal | Version | Support | Notes |
|---|---|---|---|
| iTerm2 | 3.6.9 | ✓ yes | |
| Ghostty | 1.3.1 | ✓ yes | |
| VS Code | ✓ yes | ||
| Warp | ✓ yes | ||
| Cursor | ✓ yes | ||
| Terminal.app | ✓ yes |
Headless Backends
Parser correctness only — a ✓ means the parser accepts the sequence.
| Backend | Version | Support | Notes |
|---|---|---|---|
| vterm | 0.2.0 | ✓ yes | |
| Alacritty | 0.26.0 | ~ partial | OSC 11 color query not exposed in headless mode |
| Kitty | 0.40.0 | ~ partial | OSC 11 color query not exposed via Python batch bridge |
| WezTerm | 0.1.0-fork.5 | ~ partial | OSC 11 color query not exposed in headless mode |
| vt100.js | 0.2.1 | ✗ no | Not implemented — pure TypeScript emulator |
| xterm.js | 5.5.0 | ✗ no | OSC 11 background color query not implemented in xterm.js |