it really depends on the car. some cares pull of Yellow REALLY well and others don't at ALL. But my favorite car and color combo is the 1993 Mazda Rx-7 R1 in Competition Yellow Mica.
I also like cars in Lamborghini Orange:
The blue on vipers:
It really depends on the car. I like a lot of the older cars in darker muddier colors. Liek gunmetal, British racing green, and then all of a sudden, I randomly like some cars in white a lot.