BuddyPress.org

I would do it as a settings component plugin if you want users to choose colors. Check out the groups css plugin to see how that was done if you want users to be able to add their own colors. Like Ray says, if you let users roll their own CSS then you will have the nightmare that was myspace. If it’s just pre made CSS files it’s easy to have a switch based on xprofile field. Search here it’s been asked before.