This mod allows you to randomize the car right before every single time a level loads. Quick warning, this will give you a minor annoyance in the garage. Make sure you have your favorite colors are saved as your main car's colors may get changed. This works with custom cars!
Car and colors can be randomized separately. By default, the mod has both options turned on. If you want to stop the randomization at any time then you can toggle both options off to stop the randomizing.
Settings will be remembered after closing the game.