Personally, I prefer either white or silver. Reflects the sun and keeps things just a little bit cooler in the summer. That said, as I've never bought a new vehicle, I don't use color as a factor when purchasing. As long as it's not pink or that stupid orange-brown color.
My old Cavalier, my current Camry, and my wife's Versa are all silver, so I guess that's the most popular.
My wife's old Cavalier and my Tacoma are white, so that would be next.
My Mustang is dark blue, it would never have been my first choice but when you're looking for a 16 year old car in decent shape, you'll take what you can find.
The XTerra is yellow. Many people don't like it, but that's the best color for that particular vehicle, imo.