Caswell Canada and Emerald Coatings sells a wide rage of coating additives for both powder coating and Liquid paints.  These additives are great for making your own custom colours at a fraction of the cost of buying them premixed.  You can add them in a clear base (inter-coat clear)base coat it self.  Adding the product in the coloured  base coat may require more additive, as  only some flakes/ pearls will show up on the surface and the rest will buried in the coating itself.  Adding the flakes/pearls in an inter-coat clear will take less additive but require an extra step / layer of coating.  All pearls and additives should be clear coated at the final stage to protect the additives as well as make it pop in the sun.