A slightly different take on the metallic paint feature. Here the base of the truck is black without metallic flake and the metallic paint is only used for the flames. This makes the flames pop out when you move between the truck and the light source. Since it's not so easy to fully capture the dynamic effects in screenshots, I also made an attempt at a video here:

http://youtu.be/7IWbFwR1BDQ

Technical details are included in the video description.