Great! Just working on this on the side as I do other things (namely .. adding obj/fbx/etc import for the gui 🙂 )
Here are the same materials, but with different base colors. First metallic white with solid-color blue, then the opposite combination.
Not too pleased with the metallic white, so there is yet work to do, but there is also an issue Albert found with the material layer simulation that may improve this case, as well.
In the end, the goal is to have a nice carpaint material with just a few easy parameters, which covers these sorts of cases (metallic, solid, etc), with built-in orange peel, and such.