Have been looking at this mod with trying to add different car colors and found that if you copy the team 1 folder found in GP4\saves\carsets\audi\data\cars make it team2. Then open up the hi_r8l_main and paint the car and save as hi_r8l_main_1. then open the car_audi_car1_lod_0 with GP4 3d editor by lo2k.
Now find cockpit and see it uses hi_r8l_main, add texture hi_r8l_main_1 and make it use this tex for cockpit, save and close.
Next find the config file in the same folder as team 1. change this so team 2 is used in one of the slots and save.
Then now starting the mod you will see a different colored car. Yay