It all comes down to cost. Also, if you need to do touch ups, it is 100% easier with black or white. When you add colors, trying to match those up are near impossible. Graphics cost a lot of money, and the more intricate, the more cost. Like Bill said, we spend our money on what is needed to run, not to make the car more colorful.

With that being said, if I got a sponsor that wanted a car a certain way, and they want to pay for it, then I would do that.