Use .blue() instead of .b() in textColorForBackgroundColor

[thomasjlee]

Summary

Fixes textColorForBackgroundColor using Color.b(), which returns the Lab blue-yellow channel rather than the RGB blue channel. The YIQ calculation now uses Color.blue().

Supersedes #905 and fixes TryGhost/Ghost#27797.

Changes

• Replaces .b() with .blue() in the Color Utils source.
• Rebuilds the CJS, ES, UMD, and source-map artifacts.
• Retains the distinguishing #cccccc regression case and updates its expected contrast text from white to black.

Validation

• yarn workspace @tryghost/color-utils build

• yarn workspace @tryghost/color-utils test — 11 tests passed with 100% coverage

• yarn test — lint and tests passed across all 17 SDK packages

• There's a clear use-case for this code change

• Commit messages have short titles and reference the relevant issue

• The build, lint, and tests pass

[coderabbitai]

Walkthrough

Updated textColorForBackgroundColor to use backgroundColor.blue() in the YIQ contrast calculation across source and generated builds. Updated the #cccccc test to expect black text.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Possibly related issues

• TryGhost/Ghost issue 27797 — Addresses the same .b() versus .blue() typo that caused incorrect contrast text colors.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes implement the linked issue's required fix by using the RGB blue channel and adding regression coverage.
Out of Scope Changes check	✅ Passed	The changes are limited to the color utility implementation, generated artifacts, and related regression tests.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title clearly and concisely describes the change from .b() to .blue() in textColorForBackgroundColor.
Description check	✅ Passed	The description explains the bug, implementation change, regression coverage, linked issues, and validation results.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (0b21bed) to head (c79be97).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1031   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           30        30           
  Lines         3060      3060           
  Branches       459       459           
=========================================
  Hits          3060      3060           

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[9larsons]

Reviewed the corrected RGB blue-channel implementation and generated artifacts. Added regression coverage that fails if Color.b() is reintroduced. The Color Utils build/tests, SDK-wide lint/tests, and upstream Node 20/22 checks all pass.