BuddyPress.org

It’s not a bad idea even if I’d rather have a more united navigation (and no userpages with lots of options hidden there).

The things you’re talking about should be easily done with CSS. As long as you’ve got php-files that are specific for the places you intend the color change. You’ll have to put in some new “div id” to make it happen. That means modifying BP-default-files and using them in a child theme, as far as I understand (ie copying the files over to the child).