Instructions
Start the game and go to the "Career" mode area. Then select your garage area followed by the car you would like to paint.
Select "Paint Car" from the customization menu. The paint interface will launch automatically.
Paint using bases, brushes, stamps, layers, and decals. With the exception of bases, each of these elements can be custom-shaped and tweaked to fit your perfect design. You can use the thumbstick to control size, orientation, and placement on your car. Once you have modified a creation element, you can elect to save it or dispose of it.
Select "Finish Painting" once you are finished. Your latest paint job will automatically be applied by default, but you can save as many alternate designs for your car as you want.