This is an article about 2d histogram colouring where they discuss how you get a better colouring if you set the saturation of each bin by it's (columnwise) ran

This is an article about 2d histogram colouring where they discuss how you get a better colouring if you set the saturation of each bin by it's (columnwise) rank: that is you sort all values in each column and assign a saturation of 1 to the bin with the largest count, and then progressively smaller saturations as you go down the rankings. Presumably they don't care their column wise colouring scheme makes it impossible to sensibly compare across the rows as each column gets its own colour scale. shrug