A theme for light terminals

Declare the background your users read on, let roundel pick the brand shade that reads on it, and check the result before it ships.

The default ground is near-black. On a light terminal, say so, and every hex token is checked — and the default brand tokens chosen — against white instead:

light-check.mjs

import { reportTheme } from 'roundel/contrast';
import { audit } from 'roundel/theme';

const theme = { ground: '#fdfdfd', warn: '#9a6700' };
console.log(reportTheme(audit(theme)));

node light-check.mjs

pass  error  truecolor  #a84c17 on #fdfdfd  5.56:1 (needs 4.5:1)
pass  error  256        #af5f00 on #fdfdfd  4.63:1 (needs 4.5:1)
pass  warn   truecolor  #9a6700 on #fdfdfd  4.79:1 (needs 4.5:1)
pass  warn   256        #af5f00 on #fdfdfd  4.63:1 (needs 4.5:1)
pass  ok     truecolor  #0a6b47 on #fdfdfd  6.44:1 (needs 4.5:1)
pass  ok     256        #005f5f on #fdfdfd  7.37:1 (needs 4.5:1)

error and ok were not given, so they are the brand's deep shades, the ones that read on a light ground. warn was given as a hex, so it is checked too; the default yellow would not have been, because a format name is the user's own palette.

There is no way to ask a terminal what its background is, so the choice is yours. A program that serves both can read a setting of its own and fly the matching theme; the check runs on whichever it flies.