Polyphony also sold "Special Paint" packs via PKG. In standard GT5, finding chrome or matte paint was a rarity tied to winning used cars. The DLC sold cans of paint that could be used infinitely (or in specific quantities depending on the pack), allowing for deep customization of the "A-Spec" livery style.
For those researching the technical side of GT5's expansion content, or those trying to restore a library they paid for years ago, here is a deep dive into the "PKG" phenomenon and the content it contained. Gran Turismo 5 Dlc Pkg