Appearance
256-color bg (SGR 48;5)
ESC [ 48;5;N mSGR 48;5;N sets the background to one of 256 colors. The sequence is
ESC [ 48;5;N m. Same palette as SGR 38;5 (256-color foreground): 0-15 standard/bright, 16-231 color cube, 232-255 grayscale.How this is testedautomated
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\x1b[48;5;21mX (256-color blue), verify the background blue channel > 100.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 11 of 12 terminals (92%). Not supported by: vt100.js. Part of the Modern TUI baseline. Notes: vt100.js: Not in VT100/VT220 — only 8 standard colors supported.
Supported by 12 of 14 backends (86%)
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 |
|---|---|---|---|
| Alacritty | 0.26.0 | ✓ yes | |
| Kitty | 0.40.0 | ✓ yes | |
| vterm | 0.2.0 | ✓ yes | |
| xterm.js | 5.5.0 | ✓ yes | |
| WezTerm | 0.1.0-fork.5 | ~ partial | Backend returns palette index instead of resolved RGB |
| vt100.js | 0.2.1 | ✗ no | Not in VT100/VT220 — only 8 standard colors supported |