# Text Background Color (OSC 11)

> Set and query the color of the default background, behind text with no SGR background color.

- **Sequence:** `OSC 11 ; Pt ST`
- **ECMA-48:** [§8.3.89 OSC – Operating System Command, p. 51](https://archive.org/details/ecma-48-5th-edition-june-1991/page/n64/mode/1up)
- **xterm:** [Operating System Commands](https://invisible-island.net/xterm/ctlseqs/ctlseqs.html)

`OSC 11 ; Pt ST` sets the color of the default background, behind text with no SGR background color, and `OSC 11 ; ? ST` asks what
it is. [OSC 111](https://control-codes.page/osc/reset-background/index.html.md) puts it back as it started. It is one
of xterm's dynamic colors, and works as [OSC 10](https://control-codes.page/osc/foreground/index.html.md) explains:
`Pt` is any color X11 can parse, and a further `;` in the same sequence moves
on to color 12.

A default xterm starts it as the `background` resource, white
([`charproc.c`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/charproc.c#L543)), so in the terminal the cases run in, set up
as a default xterm, it is reported as `rgb:ffff/ffff/ffff`.

libghostty-vt has it, and agrees with xterm.

## Support

| Terminal | Version | Support | Notes |
| --- | --- | --- | --- |
| VT220 | [manual](https://vt100.net/docs/vt220-rm/), 2nd ed., 1984 | No | OSC is not among the controls it recognizes ([§4.2](https://vt100.net/docs/vt220-rm/chapter4.html#S4.2)) |
| VT510 | [manual](https://vt100.net/docs/vt510-rm/), 1st ed., 1993 | No | ignores an OSC string ([chapter 4](https://vt100.net/docs/vt510-rm/chapter4.html)) |
| xterm | patch 412, [xterm-411a](https://github.com/ThomasDickey/xterm-snapshots/tree/xterm-411a) | Yes |  |
| libghostty-vt | [0f171f6](https://github.com/ghostty-org/ghostty/tree/0f171f650a1cbbd6df4a2573b6b0c7de57cc6d90) | Yes |  |
| Konsole | 26.11.70, [a24c3d71](https://invent.kde.org/utilities/konsole/-/tree/a24c3d71be3684f24d030aa2dbe9bd723d985233) | Yes | sets and answers one color; no chain |
| kitty | 0.49.1, [run in a VM](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/kitty.json) | Yes | passes the case that shows it working; ends its replies with ST where xterm uses BEL |
| foot | 1.28.0, [run in a VM](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/foot.json) | Yes | passes the case that shows it working |
| pyte | 0.8.2, [run as a library](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/pyte.json) | No | fails the case that shows it working |
| xterm.js headless | 6.0.0, [run as a library](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/xtermjs.json) | No | fails the case that shows it working |
| alacritty_terminal | 0.26.0, [run as a library](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/alacritty.json) | Yes | passes the case that shows it working |
| ConEmu | build 230724, its [documentation](https://conemu.github.io/en/AnsiEscapeCodes.html) | No | not in its [ANSI escape codes](https://conemu.github.io/en/AnsiEscapeCodes.html) |
| rxvt-unicode | 9.31, [run in a VM](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/urxvt.json) | Yes | passes the case that shows it working; writes colors as `ff00` where xterm writes `ffff` |
| VTE | 0.84.1, [run as a library](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/vte.json) | Yes | passes the case that shows it working |

## Validation

### OSC11-1: Ask for it

Input, one step per line:

```text
\e]11;?\a
```

Expected screen:

```text
|____|
reply \e]11;rgb:ffff/ffff/ffff\a
```

### OSC11-2: Change it

Input, one step per line:

```text
\e]11;#0080ff\a
\e]11;?\a
```

Expected screen:

```text
|____|
reply \e]11;rgb:0000/8080/ffff\a
```

### OSC11-3: The answer ends as the question did

Input, one step per line:

```text
\e]11;?\e\\
```

Expected screen:

```text
|____|
reply \e]11;rgb:ffff/ffff/ffff\e\\
```

### OSC11-4: RIS leaves it alone

Input, one step per line:

```text
\e]11;red\a
\ec
\e]11;?\a
```

Expected screen:

```text
|____|
reply \e]11;rgb:ffff/0000/0000\a
```

---

This is the Markdown version of <https://control-codes.page/osc/background/>. On that page every validation case runs live in libghostty-vt, the terminal emulation core of Ghostty, compiled to WebAssembly.

The validation cases are written in the notation described in <https://control-codes.page/notation/index.html.md>.