fix: improve palette text contrast on hover across all themes

[samson1299]

Fixes #6439

This pull request improves the readability of palette button labels by ensuring the text color updates correctly when users hover over buttons across all supported themes.

• Bug Fix
• Feature
• Performance
• Tests
• Documentation
• CI/CD

[walterbender]

hmm. We are migrating away from platformcolors.js. Also, please include some before/after screenshots.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.55%. Comparing base (cf5df87) to head (b607fb1).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
js/palette.js	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7655      +/-   ##
==========================================
- Coverage   54.56%   54.55%   -0.01%     
==========================================
  Files         172      172              
  Lines       57212    57213       +1     
==========================================
- Hits        31216    31215       -1     
- Misses      25996    25998       +2     

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[walterbender]

It would helpful to include some before and after screenshots.
And we are migrating away from platformcolor -- using css/tokens.css instead. It would be good to use the new approach in your changes.