I like this suggestion, although I must say I enjoy the current colors :D
I suppose it’s as easy as using different CSS files, selectable via some php / javascript so it shouldn’t take much work…
With a little work, you could make all colors customizable (is this a word? it keeps getting underlined), since there’s basically 5 colors used throughout the whole site (black, white, green, red and a shade of gray at the moment).