# Special Colors (OSC 5)

> Set and query the colors xterm can draw bold, underlined, blinking, reversed and italic text in.

- **Sequence:** `OSC 5 ; Pc ; 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)

Besides the [palette](https://control-codes.page/osc/palette/index.html.md), xterm has five *special* colors, which
it can use to show an attribute as a color instead of, or as well as, the
attribute itself:

| `Pc` | Resource | Used for |
| --- | --- | --- |
| `0` | `colorBD` | bold |
| `1` | `colorUL` | underline |
| `2` | `colorBL` | blink |
| `3` | `colorRV` | reverse |
| `4` | `colorIT` | italic |

`OSC 5 ; Pc ; Pt ST` sets one, `Pt` of `?` asks for it, and
[`OSC 105 ; Pc ST`](https://control-codes.page/osc/reset-special-colors/index.html.md) puts it back, exactly as
[OSC 4](https://control-codes.page/osc/palette/index.html.md) and [OSC 104](https://control-codes.page/osc/reset-palette/index.html.md) do for the palette; they are also palette numbers 256 to 260, so
`OSC 4 ; 256 ; ? ST` asks for the bold color too
([`do_osc`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/misc.c#L4190-L4196),
[`ReportAnsiColorRequest`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/misc.c#L2636-L2659)).
Each is used only when its mode is on, which [OSC 6](https://control-codes.page/osc/color-mode/index.html.md)
turns on and off, and all five modes are off by default. Each starts as the
default foreground
([`charproc.c`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/charproc.c#L666-L672)),
so in a terminal set up as a default xterm, as the cases are, each is
reported as black.

libghostty-vt has no special colors, and ignores `OSC 5` and palette numbers
past 255, so the cases that ask are known differences.

## Validation

### OSC5-1: The color for bold

*A known difference: libghostty-vt does not pass this case.*

Input, one step per line:

```text
\e]5;0;?\a
```

Expected screen:

```text
|______|
reply \e]5;0;rgb:0000/0000/0000\a
```

### OSC5-2: Set, and asked for through OSC 4

*A known difference: libghostty-vt does not pass this case.*

Input, one step per line:

```text
\e]5;1;#ff0000\a    # the color for underline
\e]4;257;?\a
```

Expected screen:

```text
|______|
reply \e]4;257;rgb:ffff/0000/0000\a
```

### OSC5-3: Nothing on screen

Input, one step per line:

```text
A
\e]5;0;red\a
B
```

Expected screen:

```text
|AB____|
cursor 1,3
```

---

This is the Markdown version of <https://control-codes.page/osc/special-colors/>. 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>.