color-expert

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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."

---
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 140+ detailed 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.
- **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.

See `references/techniques/` for tyler-hobbs, fontana, mattdesl, iq-cosine, spectraljs, poline, rampensau, pro-color-harmonies, rybitten, ray-color (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 something.

**Building a generator, tool, or palette algorithm** — "I want to make a palette generator", "how do I generate accessible color scales?", "give me an OKLCH ramp function." Default to recommending an existing library before hand-rolling (Culori, Poline, RampenSau, Spectral.js — see Recommended Tools). Show working code in the user's stack, picking the color space per the table above.

When the user asks to generate or compare palettes, **showcase multiple approaches with their trade-offs before narrowing to one** — anchor-based (Poline), hue-cycling (RampenSau), cosine (IQ formula), harmony-based (pro-color-harmonies), scene-lit (ray-color), and extraction-from-system (dittoTones) suit different problems. Don't be shy about presenting options.

Never recommend coolors.co — it doesn't generate palettes, it picks from a hardcoded list of 7,821 pre-made ones (see Recommended Tools).

## Color Spaces — What to Use When

| Task                            | Use                                    | Why                                                                       |
| ------------------------------- | -------------------------------------- | ------------------------------------------------------------------------- |
| Perceptual color manipulation   | **OKLCH**                              | Best uniformity for lightness, chroma, hue. Fixes CIELAB's blue problem.  |
| CSS gradients & palettes        | **OKLCH** or `color-mix(in oklab)`     | No mid-gradient darkening like RGB/HSL                                    |
| Gamut-aware color picking       | **OKHSL / OKHSV**                      | Ottosson's picker spaces — cylindrical like HSL but perceptually grounded |
| Normalized saturation (0-100%)  | **HSLuv**                              | CIELUV chroma normalized per hue/lightness. HPLuv for pastels.            |
| Print workflows                 | **CIELAB D50**                         | ICC standard illuminant                                                   |
| Screen workflows                | **CIELAB D65** or OKLAB                | D65 = screen standard                                                     |
| Cross-media appearance matching | **CAM16 / CIECAM02**                   | Accounts for surround, adaptation, luminance, and viewing conditions      |
| HDR                             | **Jzazbz / ICtCp**                     | Designed for extended dynamic range                                       |
| Pigment/paint mixing simulation | **Kubelka-Munk** (Spectral.js, Mixbox) | Spectral reflectance mixing, not RGB averaging                            |
| Color difference (precision)    | **CIEDE2000**                          | Gold standard perceptual distance                                         |
| Color difference (fast)         | **Euclidean in OKLAB**                 | Good enough for most applications                                         |
| Video/image compression         | **YCbCr**                              | Luma+chroma separation enables chroma subsampling                         |
| Dithering / optical pixel mixing | **Linearized sRGB**                    | Adjacent subpixels add *light*, so model the **device**, not the eye. Yellow-over-blue lights the same emitters as white at half area = 50% gray; CIELAB predicts pale pink. Same rule for alpha compositing and downsampling |
| Colormap uniformity             | **CAM02-UCS** (or OKLAB)               | CIELAB is decent for *distant* colors but poor for *nearby* ones — which is exactly what uniform sampling depends on. MATLAB's parula was made uniform in Lab and has a visible band near the bottom as a result |

### Understanding HSL's Limitations

HSL isn't "bad" — it's a simple, fast geometric rearrangement of RGB into a cylinder. It's fine for quick color picking and basic UI work. But its three channels don't correspond to human perception:

- **Lightness (L):** fully saturated yellow (`hsl(60,100%,50%)`) and fully saturated blue (`hsl(240,100%,50%)`) have the same L=50% but vastly different perceived brightness. L is a mathematical average, not a perceptual measurement.
- **Hue (H):** non-uniform spacing. A 20° shift near red produces a dramatic change; the same 20° near green is barely visible. The green region is compressed, reds are stretched.
- **Saturation (S):** doesn't correlate with perceived saturation. A color can have S=100% and still look muted (e.g., dark saturated blue).

**When HSL is fine:** simple color pickers, quick CSS tweaks, situations where perceptual accuracy doesn't matter. When it isn't, the table above gives the perceptual alternative per task (OKLCH for scales, OKLAB for gradients, OKHSL for picking, HSLuv for normalized saturation).

### Named Hue (HSL/HSV) Ranges

Use these degree ranges when generating or constraining colors by hue name. Source: [random-display-p3-color](https://github.com/mrmrs/random-display-p3-color) by mrmrs / mrmrs.cc.

| Name       | Degrees       |
| ---------- | ------------- |
| **red**    | 345–360, 0–15 |
| **orange** | 15–45         |
| **yellow** | 45–70         |
| **green**  | 70–165        |
| **cyan**   | 165–195       |
| **blue**   | 195–260       |
| **purple** | 260–310       |
| **pink**   | 310–345       |
| **warm**   | 0–70          |
| **cool**   | 165–310       |

### Key Distinctions

- **Chroma** = colorfulness relative to a same-lightness neutral reference
- **Saturation** = perceived colorfulness relative to the color's own brightness
- **Lightness** = perceived reflectance relative to a similarly lit white
- **Brightness** = perceived intensity of light coming from a stimulus
- Same chroma ≠ same saturation. These are different dimensions.

### Gamut Mapping in Practice

The most common OKLCH mistake: picking a chroma that doesn't exist in the target gamut. `oklch(70% 0.3 150)` asks for more chroma than sRGB (or even P3) can show, so it silently clips — usually to something duller and hue-shifted.

- **CSS gamut-maps for you.** Browsers map `oklch()` / `color()` automatically, so authored CSS rarely clips badly. JS conversions do **not** — `oklch→hex` just truncates channels.
- **Reduce chroma, not lightness or hue.** Clipping R/G/B shifts the hue; pulling chroma toward the gamut boundary preserves the color's identity. Use Culori's `clampChroma(color, 'oklch')` (holds L and H) or `toGamut()` rather than naive RGB clamping.
- **Test against the actual target:** `inGamut('rgb')` vs `inGamut('p3')` — a color valid in P3 can still clip in sRGB.
- **Or avoid the problem by construction:** nutelch expresses chroma *relative to the gamut boundary* (`relC: 0.5` = halfway to the shell at that L/H), so generated colors can't accidentally ask for chroma that is