# 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.

## 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>.