# Special Color Modes (OSC 6)

> Turn on or off xterm's use of a special color for bold, underlined, blinking, reversed or italic text.

- **Sequence:** `OSC 6 ; Pc ; Pf 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 6 ; Pc ; Pf ST` turns on, when `Pf` is not zero, or off, when it is,
xterm's use of [special color](https://control-codes.page/osc/special-colors/index.html.md) `Pc`: `0` for bold,
`1` underline, `2` blink, `3` reverse, `4` italic. While a mode is on,
text with that attribute is drawn in its special color. [`OSC 106`](https://control-codes.page/osc/color-mode-106/index.html.md) is
the same as `OSC 6`, and a pair can be repeated, `OSC 6 ; 0 ; 1 ; 1 ; 1 ST`
turning on bold and underline
([`do_osc`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/misc.c#L4197-L4248)).
The modes start as the `colorBDMode`, `colorULMode` and similar resources
say, all off by default, and nothing is answered.

The number means something else to iTerm2, which uses
`OSC 6 ; 1 ; bg ; red ; brightness ; N ST` to color its tab (see the
[iTerm2](https://control-codes.page/osc/iterm2/index.html.md) page). xterm reads the `1` and then stops at `bg`,
which is not a number, so iTerm2's sequence changes nothing there.

A case cannot see a special color mode, which changes only how text is
drawn. libghostty-vt has neither special colors nor these modes, and
ignores `OSC 6`; what a case can see, that nothing is
printed or answered, is the same as in xterm.

## Validation

### OSC6-1: Nothing on screen, nothing answered

Input, one step per line:

```text
A
\e]6;0;1\a        # bold in its special color
\e]6;0;0;1;1\a    # bold off, underline on
\e]6;1;bg;red;brightness;255\a  # iTerm2's tab color
B
```

Expected screen:

```text
|AB____|
cursor 1,3
reply none
```

---

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