You would have to paint the car in order to use it IIRC.
There's a few things about the paint shop I'm still getting used to, but a couple things that may be helpful, mostly dealing with race livery and special paint/stripe groups and name badges...
-If a car has a paint job you don't like, erasing it will return it to it's original finish or racing livery, whichever was OEM.
-If you paint just wheels, you lose any race livery or car markings, except factory stock stripes.
-SOME stock stripes can be decaled over, some can't, like the end plate on the Olds rear wing for example, it always stays gold or the hood on the SRT8, the black always stays.
-Names and badges cannot be covered, as on the BOSS 429 Mustang or the 71 Mustang. Sometimes they look like Carp too. I wish they'd fix that bit, or at least make sure they look good when decaled over.
-You can't decal on chrome bumpers. It'd be nice to be able to do license plates or bumper stickers, but unless there's a separate layer like the wing, or the bumper cover is integrated and body color like on most newer cars, you're SOL.
-If you want the factory "race" car, but with different additions, you'll have to replicate the car's livery package and then add to it, but it will have to be all done by you. Just adding decals to a "stock" car usually doesn't cause anything to go away, but changing a race livery usually makes it go bye bye. (I haven't tried just adding a decal to race livery, though why not escapes me ATM)
-As noted by eek and others, there's a noticeable grey line when applying decals over paint if it isn't perfectly aligned or is a different shape etc. "Painting" the entire car in decal material first eliminates this. I usually paint the car the decal "paint color" to help with those areas that can't be decaled. (there's a thread on the main forums about unpaintable/problem areas)
Hope there's something helpful in here... I'm sure someone has the other half covered.
