White, Silver and Gray
It seems to be that weird gray color that I hate. So many times I see a really nice Porsche, and it's that color, and I'm thinking "Why?".
Black or white
Depends on the country. Japanese buy mostly white cars. Silver was by far the most common in the UK through the 2000s. White's becoming more common here also possibly due to it not costing an extra £500-1000 on a new car.
Black or dark gray
I would say white. White is the top color for fleet sales - to corporations, government, rental businesses. Of the newer SUVs I see on the road, which is currently the #1 segment in sales, I see more white than any other color.