/skill.color-expert

name: color-expert
description: Use when working with color naming, color theory, color spaces, color definitions, or any task involving color knowledge - palettes, ramps, gradients, conversions, accessibility, perceptual matching, pigment mixing, print-vs-screen color, CSS color syntax, or historical color terminology. Use this skill whenever the user is choosing, comparing, generating, naming, converting, or explaining colors, even if they do not explicitly ask for "color theory."

Color Expert

A comprehensive knowledge base for color-related work. See `references/INDEX.md` for a one-line-per-file map of 180+ reference files; this skill file contains the essential knowledge to answer most questions directly.

How to Use This Skill

Match the response to the user's explicit request and clearly implied constraints from context. Five common modes:

**Concrete design or art project** — "help me pick colors for my logo / poster / illustration / app." Ask about medium (print, screen, paint, mixed), brand or mood, audience, accessibility needs, and any existing colors to harmonize with. Then propose. Don't lecture about CIE 1931 or OKLCH internals unless asked. Recommend specific tools and palettes that fit the constraints, not generic theory.

**Design system, ramps, or theme tokens** — "build me a 9-step accent scale", "palette for light + dark mode", "Tailwind/Radix-style ramps", "what's the right gray ramp for our brand?" Prioritize in this order:

• Use OKLCH to build perceptually uniform scales (consistent lightness across hues, no muddy mid-tones).
• Build a token graph: reference tokens (palette) → semantic tokens (surface, on-surface, accent, success, warning, danger) → component usage; see *Implementation Guidance* below.
• Verify every text/background pair against APCA or WCAG in both light and dark.
• Suggest tools only as needed: Huetone (LCH/OKLCH builder), Leonardo (contrast-ratio-driven ramps + adaptive theming, Adobe), Components.ai Color Scale (parametric), dittoTones (extract perceptual DNA from Tailwind/Radix), Color Buddy (lint). For dataviz sequential/diverging ramps specifically, CuspHanger (Wijffelaars model in OKLCH, in-gamut by construction) or viscm (the viridis editor: live perceptual-derivative diagnostics + CVD + grayscale while you drag control points).

The test for a sequential ramp is **flat perceptual derivative** — plot the perceptual step size between consecutive samples; it should be a horizontal line, in color *and* in grayscale. Bumps are regions where the ramp exaggerates change that isn't in the data (this is jet's core failure, not its ugliness).

**Generative art / creative coding** — "color for my fxhash piece", "palette for thousands of generated strokes", "paint-like mixing in p5.js / WebGL." Different from building a palette generator: the code *is* the artwork, and the user wants to understand the *techniques*, not copy a named artist's style. Help them compose their own system. Useful techniques to teach and combine:

• **Tight constraint, then variation** — pick 3–7 hues in a narrow lightness or chroma band; variety comes from density and interaction, not palette size.
• **Weighted / probability-based hue selection** — assign each color a weight so some appear often, others rarely; this is what makes a generative output feel curated instead of random.
• **Narrow-band hue jitter** — small random hue offset within a fixed envelope keeps strokes feeling related but not identical.
• **Lightness variation at fixed chroma** — depth and atmosphere without losing palette identity (use OKLCH).
• **Spectral / K-M mixing** (Spectral.js, Mixbox) for paint-like overlap and secondaries; RGB averaging gives muddy, dull results in the same situation.
• **IQ cosine palette** — `a + b·cos(2π(c·t + d))` for cyclic / periodic schemes from 12 floats.
• **Anchor-based interpolation** (Poline) — set 2–3 anchors in OKLCH, get an interpolated ramp.
• **Hue / lightness / chroma trajectories with easing** (RampenSau) — walk each axis along an easing function, color-space-agnostic; great when you want a deterministic ramp shape rather than random anchors.
• **Harmony-aware generation with muddy-zone avoidance** (pro-color-harmonies) — adaptive OKLCH harmony with 4 styles × 4 modifiers; skips perceptually muddy regions automatically.
• **Generation in historical / non-digital color spaces** (RYBitten) — work in RYB or one of 26 historical color cubes when you want a painterly feel that strict sRGB/OKLCH can't reach.
• **Palette cycling / indexed color** — store an index buffer and a small palette, then animate the palette (rotate, ease, or drive from an OKLCH trajectory) instead of the pixels; motion for one lookup per pixel. Works only if each cycle range is a perceptually even closed ramp. See `references/techniques/color-cycling-indexed-palette-animation.md`.
• **Scene-light sampling** (ray-color) — raytrace a sphere in a room with up to 3 colored lights and sample colors off its surface; coherence comes from shared illumination physics (like an object photographed under one light) rather than color-space geometry.
• **Sun-lit ramps** (Lightfield, tol.is) — same idea aimed at design tokens: OKLCH pigments on a flat-shaded city under a Planckian-locus sun; each 50–950 ramp is a sweep of surface orientations, re-spaced in L. Adds relative chroma, cusp pull, and a hue-profiled Bezold–Brücke/Abney warm shift (toward red going dark, toward yellow going light; cool hues untouched).

See `references/techniques/` for tyler-hobbs, fontana, mattdesl, iq-cosine, spectraljs, poline, rampensau, pro-color-harmonies, rybitten, ray-color, lightfield (these document the techniques, not styles to imitate).

**General color question** — "what is OKLCH?", "why does my gradient go gray in the middle?", "is APCA better than WCAG?" Answer directly from this skill file or `references/INDEX.md`, and cite the relevant reference. Skip tooling unless they're asking how to do someth