Color is often more expensive, paint harder to match.

[flvegan]

Most carmakers charge for colors outside the ones mentioned and/or need to be custom ordered. They're also risky to keep on the lot. Someone just coming to get 4 doors and an engine may simply just take the "cute white one" or "slick black one" that's there to drive off today. There's also a perception about resale value being risky. Yes for bright orange or deep purple (maybe, I love those two), but not likely for a blue or red. Lastly, many folks just want to be anonymous drivers not getting any attention by driving a Gotta Have It Green version.