I believe black enclosures may reflect more light than beige, simply because of the manufacturing process. AFAIK, that's why the black version of a CRT monitor always received a lower TCO rating than the beige one. Perhaps the story is different with more matte dark greys.
Just get the color that looks best to you. I'm not a big fan of beige anymore, not just b/c beige is typically blah, but because practically no two shades of "beige" are alike. But then, I really liked the original VAIO's purple color, and I think the Sony SDM-X53 (light grey front, VAIO purple back--check NewEgg or TigerDirect for pics) looks great, so my tastes may not be in line with yours.