Adobe Leonardo Contrast Colors — Agent Skill
When helping users with @adobe/leonardo-contrast-colors, follow these steps. For full API details (parameters, types, setters), load references/api.md on demand.
1. Installation
npm i @adobe/leonardo-contrast-colors
ESM (recommended):
import { Theme, Color, BackgroundColor, contrast, convertColorValue, luminance, createScale } from '@adobe/leonardo-contrast-colors';
2. Creating Color and BackgroundColor
BackgroundColor
One per theme. Defines the background and the scale of grays (or other neutrals) at target ratios.
const gray = new BackgroundColor({
name: 'gray',
colorKeys: ['#cacaca'], // one or more keys to interpolate
ratios: [2, 3, 4.5, 8] // target contrast ratios (positive = darker than background)
});
Color (foreground)
Defines a semantic color (e.g. blue, red) at specific contrast ratios.
const blue = new Color({
name: 'blue',
colorKeys: ['#5CDBFF', '#0000FF'], // interpolated in colorspace
colorspace: 'LCH', // optional; default 'RGB'
ratios: [3, 4.5] // e.g. large text (3:1), normal text (4.5:1)
});
Parameters:
- name — Used to prefix output names (e.g.
blue100,blue200). - colorKeys — Array of CSS color strings; the scale is interpolated between them.
- colorspace (or colorSpace) — Interpolation space:
'LCH','LAB','RGB','HSL','HSV','HSLuv','CAM02','CAM02p','OKLAB','OKLCH'. Default'RGB'. - ratios — Either an array of numbers (e.g.
[3, 4.5, 7]) or an object mapping custom names to ratios (e.g.{ 'blue--largeText': 3, 'blue--normalText': 4.5 }). - smooth — Optional boolean; bezier smoothing for interpolation (default
false). - output — Optional output format (default
'HEX'); usually overridden by Theme.
Negative ratios — Use negative values (e.g. -1.5, -3) for colors lighter than the background (e.g. text on dark mode). Naming for negatives uses fractional increments (e.g. gray25, gray50).
3. Creating a Theme
Combine one BackgroundColor and one or more Colors with a lightness and optional contrast/saturation.
const theme = new Theme({
colors: [gray, blue, red], // gray is BackgroundColor; blue, red are Color
backgroundColor: gray, // required; must be the BackgroundColor instance
lightness: 97, // 0–100; background lightness (e.g. 97 = light, 8 = dark)
contrast: 1, // optional; multiplier for all ratios (default 1)
saturation: 100, // optional; 0–100 (default 100)
output: 'HEX', // optional; default 'HEX'
formula: 'wcag2' // optional; 'wcag2' (default) or 'wcag3' (APCA)
});
Note: colors should include the same BackgroundColor as the first element (or at least include it in the list) plus all foreground Colors. The Theme requires backgroundColor to be set to that BackgroundColor instance.
4. Reading theme output
Three getters:
- theme.contrastColors — Array: first element
{ background: '#...' }, then one object per color withnameandvalues: [{ name, contrast, value }]. Use for design tokens or CSS variable generation. - theme.contrastColorPairs — Flat object:
{ gray100: '#e0e0e0', blue100: '#b18cff', ... }. Use for quick lookups. - theme.contrastColorValues — Flat array of color strings only.
Example iteration for CSS variables:
for (const item of theme.contrastColors) {
if (item.background) {
document.documentElement.style.setProperty('--background', item.background);
} else {
for (const v of item.values) {
document.documentElement.style.setProperty(`--${v.name}`, v.value);
}
}
}
5. Mutating a theme at runtime
After construction you can change:
- theme.lightness = 8 — e.g. switch to dark background.
- theme.contrast = 1.2 — increase contrast globally.
- theme.saturation = 80 — reduce saturation.
- theme.output = 'RGB' — change output format.
- theme.backgroundColor = otherBackgroundColor — swap background (pass BackgroundColor instance).
- theme.colors = [gray, blue, red, green] — replace color list.
Adding/removing/updating colors:
- theme.addColor = newColor — Add a Color instance.
- theme.removeColor = { name: 'red' } or theme.removeColor = redColorInstance — Remove by name or by instance.
- theme.updateColor = { name: 'red', ratios: [3, 4.5, 7] } — Update a color’s ratios (or colorKeys, name, etc.) by name.
After any setter, re-read theme.contrastColors (or pairs/values); they are computed on access.
6. Utility functions
- contrast(foregroundRgbArray, backgroundRgbArray, baseV?, method?) — Returns contrast ratio.
method:'wcag2'(default) or'wcag3'. RGB arrays are[r, g, b](0–255). Use to check two colors without building a full theme. - convertColorValue(colorString, format, object?) — Convert any supported color string to
format(e.g.'HEX','RGB','LCH'). Ifobject === true, returns channel object instead of string. - luminance(r, g, b) — Relative luminance (0–1) for sRGB.
- createScale({ swatches, colorKeys, colorSpace?, shift?, fullScale?, smooth?, distributeLightness?, sortColor?, asFun? }) — Build an interpolated scale (no contrast targeting). Returns array of color strings unless
asFun: true(returns scale function). Useful for non-accessible palettes or stepping between keys.
7. Common accessibility recipes
- WCAG 2 AA (normal text) — Minimum 4.5:1. Use
ratios: [4.5]or include 4.5 in ratios. - WCAG 2 AAA (normal text) — Minimum 7:1. Use
ratios: [7]or include 7. - WCAG 2 large text — Minimum 3:1. Use
ratios: [3]or include 3 for large text tokens. - WCAG 2 AA + large text — Use
ratios: [3, 4.5]and name via object if desired:{ 'brand--large': 3, 'brand--normal': 4.5 }. - WCAG 3 / APCA — Set
formula: 'wcag3'on Theme. Interpret APCA Lc values per WCAG 3 guidance; the library returns Lc for contrast when method is'wcag3'.
Recommendation: Prefer LCH or LAB for interpolation (colorspace: 'LCH') for perceptually even scales.
8. Supported colorspaces and output formats
Interpolation colorspaces (Color/BackgroundColor colorSpace, createScale):
LCH, LAB, RGB, HSL, HSV, HSLuv, CAM02, CAM02p, OKLAB, OKLCH.
Output formats (Theme output, Color output, convertColorValue):
HEX, RGB, HSL, HSV, HSLuv, LAB, LCH, CAM02, CAM02p, OKLAB, OKLCH.
Values follow W3C CSS Color Module Level 4 (e.g. lch(100% 0 360deg), rgb(255 255 255)).
For full parameter tables, setter lists, and type details, see references/api.md.