I wanna colour code my plastic bumpers on my uno, would i prime it a few times then just spray the paint on or will it peel off.

best thing to do would be to use some high-build primer, so it fills in the injection moulded "bumpy" effect - if this is painted straight on then it will give a matt effect. make sure the stuff you use is plastic compatible...

paint and then lacquer over the top - but it's best to hand wash the car after you do that, I've coloured a fair few bits of my car and I wouldn't trust car washes now... not sure how much paint would be left on the bits... (car manufacturers bake the paint on by using a high temperature paint booth, and it's unlikely you'll be doing this yourself)