looked at my history, and it was gold, brown, red, red, maroon, red, black, blue, black, blue, silver, red, black, green, brown, tan, blue.
So red is the most common, but not by choice. Just happened that the vehicle I bought was red.
I have only had one vehicle purchase (2001 Ram 1500) that I had a color choice with, I wanted the electric blue, but the wife convinced me I wanted the black instead (and really liked the black when clean, but a pain otherwise).