Make a colour scheme of your own

themes in ~/.mulmoterminal/config.json defines schemes that appear in Settings' picker next to the four built-ins, and that a project can then name in its .mulmoterminal.json theme key. Settings can choose a theme; nothing in the app can create one. This skill is that path.

This is the whole app's palette — panel backgrounds, borders, accent, text. A single project's badge and header colours are a different thing (mulmoterminal-dirs).

How to run this

1. Find out what they're going after

Ask for the direction first, with concrete options rather than "what colours?":

• From something that exists — a painting, a photo, a brand, an editor theme they like. This is the easiest to do well: take 5–8 colours off the source and assign them to roles.
• A variant of a built-in — "Nord but warmer", "Daylight with more contrast". Use extends and write only the keys that differ.
• Light or dark, if it isn't already obvious. It decides every value below.

2. Decide extends — and know what it costs

{ "id": "arles", "label": "Van Gogh (Arles)", "extends": "daylight", "colors": { "--accent": "#c8971e" } }

• With extends, colors is a diff over that built-in (midnight / nord / daylight / solarized). Anything you leave out is inherited. Start here — it is far easier to get right, and a three-key diff is a real theme.
• Without extends, the theme must set every one of the 20 keys below. This is enforced when the config is saved, not when the theme is painted: an incomplete theme with no base is rejected outright rather than half-applied, because the missing half would inherit whatever the previous theme left on the element.

3. Write the colours

Assign the source's colours to roles, then say what each one is doing before you write it. Rules that matter more than taste:

• --text on --bg-base and --bg-panel must stay readable. Check the WCAG contrast ratio: gamma-decode each channel (c/255, then c<=0.03928 ? c/12.92 : ((c+0.055)/1.055)^2.4), weight 0.2126 R + 0.7152 G + 0.0722 B, ratio (lighter+0.05)/(darker+0.05). Aim for 4.5:1 or better for --text, and don't let --text-muted fall below 3:1 — a beautiful palette that can't be read is the usual way this goes wrong.
• --on-accent goes on --accent-bg, not on the page. Check it against that, and nothing else.
• A painting's colours are rarely usable raw. Backgrounds want the muted, desaturated end of the source; the accent wants its most saturated note. Taking six vivid colours and putting them in six roles produces something unusable at 12px.

4. Write, then look

themes is a partial POST /api/config merge — write only themes, so the user's other settings survive. Send the whole array, existing entries included: it replaces, it does not append, and a lone new entry silently deletes the rest.

Then: reload the tab, open Settings, and pick the theme. It does not appear until the page re-reads the config. If the file was hand-edited while the server was running, the server needs a restart too.

Ask what to change and adjust. The picker is the real preview — apply and look, rather than describing.

5. Offer to pin it, if that's what they meant

A theme is global. If the user wanted "this project in my new scheme", the second half is "theme": "<id>" in that project's .mulmoterminal.json — hand off to mulmoterminal-dirs.

Schema

{
  "themes": [
    { "id": "arles", "label": "Van Gogh (Arles)", "extends": "daylight", "colors": { "--accent": "#c8971e" } }
  ]
}

id must not be a built-in id. midnight, nord, daylight and solarized are refused rather than merged into — someone reading the guide's description of Midnight has to get Midnight.

The hex shape is doing security work, not tidiness: these values land in CSS custom properties, so a value that escaped the hex shape would be injected into a style declaration. Never write anything but a hex literal here — no var(...), no color-mix(...), no named colours.

The 20 keys

When it doesn't take

Work down this list before changing colours:

• The theme isn't in the picker — the tab hasn't been reloaded, or the entry was dropped in validation. Settings names a selected-but-undefined theme explicitly; that message is the tell.
• Nothing changed after picking it — an extends-less theme missing keys never reached the config at all. Re-read ~/.mulmoterminal/config.json and see whether the entry is actually there.
• The whole array vanished — a partial write. Always send themes complete.
• One colour ignored — a key outside the 20, or a value that isn't a hex literal.