There were only 12 colors that Hot Wheels used to paint their cars with. But, because of the spectraflame process that they used to paint them, there are many variations in the colors. Depending on who you talk to there can be 20 or more different colors recognized by collectors. For example brown can be broken into pale brown or dark brown depending on how thick the paint was applied at the factory.
The Custom Volkswagen can also be found painted in the enamel colors of:
green 
magenta 
red 