256-color bg (SGR 48;5)

Category: sgr · Tags: Xterm Extensions · Specification ↗

ESC [ 48;5;N m

SGR 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 tested: Send \x1b[48;5;21mX (256-color blue), verify the background blue channel > 100.

Analysis2026-03-26

Supported by all 8 tested terminals — universal adoption. Part of the Modern TUI baseline.

Supported by 11 of 13 backends (85%)

Terminal Applications

Terminal	Version	Support	Notes
iTerm2	3.6.9	✓ yes
Ghostty	1.3.1	✓ yes
VS Code	1.112.0	✓ yes
Warp	0.2026.03.18.08.24.03	✓ yes
Cursor	2.6.21	✓ yes
tmux	3.6a	✓ yes
Kitty	0.46.2	✓ yes
Terminal.app	2.15	✓ yes
GNU Screen	5.0.1	✓ yes

Headless Backends

Parser correctness only — a ✓ means the parser accepts the sequence.

Backend	Version	Support	Notes
Alacritty	0.26.0	✓ yes
vterm	0.2.0	✓ yes
WezTerm	0.1.0-fork.5	~ partial	Backend returns palette index instead of resolved RGB
vt100	0.2.1	✗ no	Not in VT100/VT220 — only 8 standard colors supported

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