This bug refers to the dialog that can be accessed clicking on a color in the third item in the toolbar (to the right of "Fill Patterns").
CMYK : There is significant mouse offset in the visual selector
L*a*b* : There is no visual selector shown. Clicking in the area where it would be will change the selected color and several messages from QPainter will be printed to the terminal.
Yeah, I recall seeing these.
This was recolved by Lynx3d's refactor.