I wanted to create a more flexible car paint "shader". Import the NodeTree from this .blend file to use it.
You can set difuse color, difuse absorption color, pearlescent color and particle size, metallic color and particle size, pearl/metal mix (particle bias) and clearcoat color. You can also plug the Displacement map output into the displacement to get an "orange peel" look, and set both the amount of the effect and the size of the map (Rugosity and Rugosity Size).
The blend file contains the NodeTree, so if you open it you won't see anything.