3) We could use one, two or three colors. One color is best. I don't care which one is used, but one color is best.
(1) and (2) are both correct and mean pretty much the same thing.
(3) says that it is possible to use as many as three (unspecified) different colors, but that in your mind, it is best to use only one, no matter what that color is. It could be the color of baby poop, but that's better than using more than one color.
(4) doesn't make a whole lot of sense to me. What does it mean to you?
Thank you very much, DocV,
I thought that '4' might mean the same as '3' as well as being a self-contradictory statement. Apparently it has only one meaning and that meaning is self-contradictory.