Maybe this is a setting I just haven’t noticed yet, but all my tasks are the same color when I’m looking at the board. I don’t see the color I assigned to them unless I get in to edit them. I wasn’t to see yellow and blue out on the board.
Have you installed any custom theme that modifies the task colors?
KanboardCSS might be the culprit.
Never used it; I cannot help.
But be careful with using unmaintained plugins on actual Kanboard versions.