Metallic skins? Irridescent skins?

[Vaughn Stegeman]

Hiya. Me again with yet ANOTHER question.
I've seen a bunch of cars with very very nice looking metallic skins. I'm not seeing how to do that with standard skinning methods, i.e. painting a skin in a graphics app.
Any tips on how to do this please? Particularly leaving some parts bare metal while other parts are painted.
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Another one I'm curious about is iridescent paint jobs. The ones where, from certain angles, it seems like there's another color over the primary base color.
Also really curious is sparkly paint jobs can be done, and if so how?
I know these are probyobaboly pretty advanced skinning techniques, but then I'm pretty well versed in computer graphics. A curious mind wants to know.
Thanks in advance!!