[pbroom]

Option-less mix() interpolated the raw hue of achromatic endpoints, so
mix(white, #0000ff) landed at h=312.03 while interpolate() (and
colorjs.io) give 264.05. Three different achromatic cutoffs were in use
(1e-4 in OKLab->OKLCH, 1e-3 in option-less interpolate, 4e-6 in the CSS
interpolation path), and the sRGB transfer function was written three
times with different sign handling.

• Add ACHROMATIC_CHROMA_THRESHOLD (0.000004, the CSS Color 4 OKLCH
  epsilon) and isAchromatic() in utils, exported from the root. Every
  8-bit/float gray converts with chroma ~1e-15 and the least chromatic
  non-gray 8-bit color has chroma ~0.00106, so the cutoff separates them.
• Option-less mix()/mixInto() now delegate to the same OKLCH default as
  interpolate()/generateScale(): a powerless endpoint borrows the other
  endpoint's hue, both powerless gives h=0, and input hues are normalized
  before the shortest-arc fix-up. mix, interpolate and generateScale now
  agree, and match colorjs.io for gray endpoints in every space.
• OKLab->OKLCH conversion keeps reporting h=0 for achromatic results
  (now at the shared threshold). Color.h stays a number: a rectangular
  source has no hue to preserve, and atan2 of float residue is noise, so
  0 is the canonical achromatic hue. Chroma is left as computed. Hues of
  OKLCH inputs are never rewritten; interpolation treats them as
  powerless when chroma <= threshold instead.
• linearToSrgbChannel()/srgbToLinearChannel() in utils are now the one
  sign-preserving, extended-range transfer pair (CSS Color 4/colorjs.io),
  used by conversion/p3, interpolation, interop kernels, srgb and gamut
  linear bounds. In-range results are unchanged.
• Property tests (fast-check): hue in [0, 360), mix(a,b,0)~a,
  mix(a,b,1)~b, option-less mix/mixInto/interpolate/generateScale
  agreement, option-less vs { space: 'oklch' } agreement, and transfer
  pair oddness/invertibility; plus colorjs.io checks for gray endpoints.

Part of a stacked set of PRs (#204 → #221) from the color-kit assessment. Validated per branch with pnpm build and pnpm test; lint, format, typecheck, size, artifact, preprod and agents checks pass at the top of the stack.

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[pbroom]

• refactor(react)!: remove UI components; ship state and plane hooks only #249
• docs(react): rebuild the React docs around the plane hooks #248
• feat(react): add plane renderer, geometry and adaptive-quality hooks #247
• feat(docs): syntax highlighting palette for code samples #246
• feat(docs): native API map at /api/map #245
• docs: add concept pages, guides and entry-point narratives #244
• feat(docs): live plane hero on home and the example system #243
• feat(docs): generated API reference from TypeDoc JSON #242
• refactor(core)!: derive plane query budgets from step counts and drop PlaneWithSense #241
• fix(react): render input aria-label once, on the inner input #240
• fix(driver): map absolute percents as range positions and keep tiny-step precision #239
• fix(core): uncap saturate chroma and resolve planeHue as an OKLCH hue #238
• fix(driver): reject unknown gamuts and align validation error types #237
• chore(docs): remove Sandpack, the shadcn kit and the legacy docs shell #236
• docs(core,driver,react): document the public API #235
• chore: pin control-kit to a commit with its own pnpm workspace #234
• docs: update implementation backlog for the contrast solver replacement #232
• refactor(react)!: remove ColorPlane's deprecated edge option and webgl renderer alias #231
• fix(driver): validate the gamut in getColorAreaFallbackPoint #230
• feat(driver,react): keep the previous hue when an achromatic color is entered #229
• refactor(core)!: replace the hybrid contrast solver with chroma-column tracing #228
• perf(core): trim what contrastRatio pulls in #227
• perf(core): pack the named-color table #226
• feat(core): point 'p3' users to 'display-p3' #225
• chore: ignore local .claude files in prettier #224
• refactor(core)!: retire the legacy contrast-region engine #223
• fix(core): keep hybrid contrast contours connected through folds #222
• chore: add changesets for the assessment stack #221
• docs: generated API reference and repo polish #220
• chore: adopt changesets for versioning and release notes #219
• chore: fix facade peers, licensing, and lint ignores #218
• refactor(react): reuse core contrast and transfer functions #217
• refactor(core)!: make the contrast-region engine explicit #216
• refactor(core)!: remove pre-launch aliases and trim the root export surface #215
• refactor!: name the Display P3 space 'display-p3' everywhere #214
• refactor(driver): share pointer drag throttling between slider and area #213
• feat(react): keyboard, ARIA, disabled, and focus support for sliders and areas #212
• fix(react): stable refs, WebGL context loss, and handler composition #211
• fix(react): apply controlled updates against the latest snapshot #210
• feat(core): selectable gamut mapping method #209
• fix(core): compute contrast from unrounded values #208
• fix(core): consistent achromatic hue handling and single transfer function #207 👈 (View in Graphite)
• feat(core): parse CSS Color 4 syntax #206
• fix(core): reject malformed color input instead of producing NaN #205
• chore: add fast-check and axe-core test dependencies #204
• docs: graphics and performance APIs demo page #203
• feat(core): tuple and typed-array interop for GPU and three.js #202
• feat(core): allocation-free *Into variants for hot paths #201
• feat(core): interpolation space option for mix/interpolate/generateScale #200
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[greptile-apps]

Confidence Score: 4/5

[Medium risk] Standardizes achromatic hue handling across interpolation paths.

The PR should not merge until option-less mixing preserves its documented exact endpoints.

Findings

1.  Endpoint hue is replaced ▶

Summary

The PR unifies achromatic-hue decisions across conversion and interpolation, consolidates extended-range sRGB transfer functions, and adds regression and property tests.

• Option-less mixing now uses the same default OKLCH helper as interpolation and scales.
• Exact endpoint hue preservation needs correction in that shared path.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A["mix / mixInto"] --> D["Default OKLCH helper"]
  B["interpolate / generateScale"] --> D
  D --> H["Shared powerless-hue threshold"]
  C["Mix with options"] --> E["Space interpolation"]
  E --> H
  D --> R["Endpoint result"]
  E --> X["Exact endpoint copy"]

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Project	Deployment	Actions	Updated
color-kit	Ready	Preview	Oct 10, 2026 7:09pm UTC

[pbroom]

Merge activity

• Oct 10, 6:47 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Oct 10, 7:02 PM UTC: Graphite rebased this pull request as part of a merge.
• Oct 10, 7:02 PM UTC: @pbroom merged this pull request with Graphite.