this has been mentioned and discussed before.
i think it really depends on the State. here in Indiana, when you go to 'register' your car and get your plate (tag as some call it), the BMV will ASK you "what color is your car?"
when i do my While/Black Passion, i'm telling them "Black" as that is the only part of the car that is PERMANANT. the way i see it, all the 'White' pieces are 'trim' and should not be considered part as the color of the car.
but that's just MY opinion......