Thanks AlienTwo, I'll give that a go in a minute.
Like others have said, it depends on the car in question. My favourite colour scheme is Bright Purple metallic with Ice White pearlescent. Then I go with Gold or Anthracite Black wheels. So a car which gets that paint job doesn't change.
Otherwise, I change colour on my car every week or two. Going through a Matte White primary/Red or Dark Blue secondary colour scheme at the moment.