2 of my parents' friends are insurance agents. They said that they (State Farm) has done extensive studies with car color and insurance risks. Here's a rough breakdown:

Black: Harder to see in the dark, so the accident risk increases(I guess they ignored the headlights).

Grey/Silver/Brown: Match road color, so they're more likely to be struck by an inattentive driver.

White: Harder to see in snow, and thus more accident prone.

Red/Yellow: More visible, and thus more likely to be pulled over for speeding, etc.

So, no matter what color your car is, you're SOL if the above is true. There are additional (hidden) premiums based on model, color, and geographic region - like white in Wisconsin. But, overall, the premium adjustments are small, so get whatever color you like best.