I think a pearl or metal flake white OR black would looks pretty darn nice. I actually saw a white metal flake C5 at one of the shows that looked absolutely stunning. And more than once, I wished that the black on the C5 and C6 was a metal flake metallic type paint. I just like that look in a paint.
Of course, I really like the new Cyber Metalliic Gray (or whatever it is they call it) that they have come out with for 2009. I may be tempted to trade in the 2007 C6 for one next year.