Computers should have been black, just like all audiovisual equipment today. How they ended up beige is an evolutionary aberration.
Before going any further, I must give honorable mention to Silicon Graphics for coming up with cool case designs nine times out of ten, long before the iMac came out.
What I'd like to see, though, to end the reign of beige through pure excess, is hotrod-style computers. Stylized flames, painted-on mouths full of sharp teeth, aerodynamic shapes and, most of all, chromed exhaust pipes running up the sides. But whatever you do, do not -- I repeat: do not -- call them "extreme" computers (or X-treme, or whatever the cool spelling is right now).