For the black car, the only change I made was diffuse color = black instead of yellow. If you have to do *anything* to deal with a totally different color besides changing that color, then the shader is not right.

I also changed the composition, so that there were a lot more opportunities for reflections at a shallow angle. These reflections, obeying the Fresnel reflection equation, are stronger because we're viewing them edge-wise.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)