Good thinking. We could have a main, or background color (used for most 3d elements), and then the shadows and highlight are calculated from that. I.e. add/remove [this] amount of brightness from the background color to achieve the bevels. Then there could be a foreground color which is used for titlebars and menu highlights. Plus of course titlebar text and highlight text. After that we'd only need two more colors: titlebar gradient and desktop background. That's pretty much all there is to a classic color scheme. That's five different colors. Would be super if you could just select those five colors and have an entire color scheme (you could of course tweak it later on, but that'd make things much easier).