Colours gain a CIE Lab model (`Color::Lab {l,a,b}`, serde tag `lab`), handled through the
CMS (display, separation, conversions, gamut), tints (toward paper white), keep_model, harmonies,
recolouring, blends, Info and the Color panel. Swatch Options gets a Lab mode
(`swatch.edit {mode: "lab"}` / `{color: {l,a,b}}`), and colour params accept `{l,a,b}`.
Swatches panel → Spot Colors… (`ui.spotColors`, dialog `spotColors`) runs `swatch.spotOptions
{useLab}` (Document.spot_use_lab, default on): Lab spot colours show and separate from their Lab
values, or art linked to them takes their working-CMYK equivalents, as one undo step. PDF export
writes Lab spot inks as Separation spaces with a Lab alternate (tint function from paper white),
or a DeviceCMYK one with CMYK equivalents.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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