[bitL]

How is color distance computed for these? Still Euclidean or a different measure? Euclidean on RGB leads to "grayification" of colors.

[arthur2e5]

On the original OKlab Euclidean will do. Perceptually-uniform color spaces are designed for that (at least for close colors).

On these slightly squished and stretched ones… I think converting back to OKlab is the better idea. You can just turn the polar stuff into Cartesian directly too, but it will be distorted.