^ I've shot vinyl before with SEM out of the can with zero prep other than giving it a dry wipe to get dust off it. It worked awesome. Dyed it 100%.

 

^^^
Yep, but for 15 bux for prep, why take a chance on fish eyes, or peeling problems....I've never had a problem with SEM, but I've always used the prep first, so I couldn't say what happens without it. Probly be ok.
I've made some cool paints, by applying several thin layers of different colours....looks a bit spotty real close up, but from any kind of distance, it can match pretty well...not as good as mixing it the right colour, but if you don't have air, a gun, etc, then it can work ok...try a test piece or two...can get some neat effects...

 

I actully found a place the supplies factory match vinyl. It was a little more expensive and dosent stretch quite as well as the HF vinyl but the colour is dead spot on.