# Tektronix Cursor Color (OSC 18)

> Set and query the color of the cursor in xterm's Tektronix 4014 window.

- **Sequence:** `OSC 18 ; 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 18 ; Pt ST` sets the color of the cursor in xterm's Tektronix 4014 window, and `OSC 18 ; ? ST` asks what
it is. [OSC 118](https://control-codes.page/osc/reset-tek-cursor/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 19.

The Tektronix colors belong to xterm's second window, which emulates a
Tektronix 4014 graphics terminal and is opened from a menu or with
`CSI ? 38 h`. They can be set and asked for whether or not that window is
showing.

A default xterm starts it as the text cursor's color
([`charproc.c`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/charproc.c#L11558-L11560)), so in the terminal the cases run in, set up
as a default xterm, it is reported as `rgb:0000/0000/0000`.

libghostty-vt has no such color, and ignores `OSC 18` and `OSC 118`,
so the cases that ask are known differences.

## Validation

### OSC18-1: Ask for it

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

Input, one step per line:

```text
\e]18;?\a
```

Expected screen:

```text
|____|
reply \e]18;rgb:0000/0000/0000\a
```

### OSC18-2: Change it

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

Input, one step per line:

```text
\e]18;#0080ff\a
\e]18;?\a
```

Expected screen:

```text
|____|
reply \e]18;rgb:0000/8080/ffff\a
```

---

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