Tamiya PS-55 Flat Clear (Lexan specific, made to complete one of they're Porsche GT3 kits, the real car is Flat Black and Gold etc...) sprayed on the outside of the body. Make sure you don't spray over areas that you do not want to be matte. If the body still has the clear overspray film on it then you can cut out the areas you want to spray with the Flat paint. If not just make the windows...etc.