Feel like this should be an option for almost every car from FH5 onwards. Here are a few examples:
- the upcoming C8 E-Ray should have an option to change the color of its trim panels on the front bumper and its side and rear vents.
- the Agera RS pinstripes should be paintable.
- the chrome trim on nearly all classic cars should be either removable or tintable.
those are just a few ideas I have.