[AlbertoFabbri93]

Coloring a layer by a categorical obs column paired the palette in uns["<column>_colors"] with the column's categories using a strict zip. When the table rows annotating an element do not use every category, the colors of the unused categories have already been dropped from the palette while the column still declares all of them, so the zip raised:

ValueError: zip() argument 2 is shorter than argument 1

Pair the palette with the used categories when its length matches theirs, so each category keeps its color. If the palette matches neither the full nor the used category list, raise an error naming the palette, its number of colors and the number of categories.

Add a test that colors a labels layer by a column with four categories, two of them used, and a two-color palette.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.17%. Comparing base (69105e0) to head (1e466a0).
⚠️ Report is 73 commits behind head on main.

Files with missing lines	Patch %	Lines
src/napari_spatialdata/_widgets.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #409      +/-   ##
==========================================
+ Coverage   63.08%   72.17%   +9.09%     
==========================================
  Files          19       19              
  Lines        2636     3404     +768     
==========================================
+ Hits         1663     2457     +794     
+ Misses        973      947      -26     

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