I'm sure the recipe for this is fairly standard? Not that I've been able to find anything googling. I need to make one up though, as I guess has been noted the CarPaint shader doesn't really work well with HDRs and DomeLights, what I'm going to get when I try to adjust something seems almost random.
I'm trying to get a fairly dark maroon-ish red with brighter red candy and/or flakes. The controls seem to be so sensitive in a domelight-lit scene that I either get solid maroon, solid fire-engine red (even though my "candy" might be imperceptibly brigther,) or uniform "flake" fuzz that looks like some sort of noise filter.
I did a larger render and the 'gaussian blur'-looking metallic "flake" effect looked somewhat better...the main problem here is that the material just doesn't behave well with HDR, but it's also partially that old issue that procedural textures really need the adjustable "filtering" feature of the Advanced Bitmap Texture.