Yes, but that isn’t same as purpose 
What ever. I just don’t believe users can and will identify categories per different colors, so I have disabled them where I can and otherwise I tried to use same color forum wide. I don’t see any other purpose for category colors than decorative aspect and that is purely matter of taste.
And that’s why I would very much like to get an option to disable those at the sidebar as I can on rest of a forum.