Remember how psyched we all were when Gmail recently let you change your theme? The only thing that was missing, it seemed, was the ability to just do simple custom colors. Well, four months later, you can now do just that.
You'll find the color editor with the Gmail themes; select it, and you can pick a color for just about everything. Mix and match, coordinate, go nuts. I went for a lovely Spring palette so my email can lift me out of my Winter doldrums.