If you want a perfect match, you'll have to repaint the bumper as well. Pearl and metallic paint jobs have little bits of metal or mother of pearl in them, which when being sprayed are layed down in a uniform way. if you were to just paint the lip, your color and pearl would be off. maybe not horribly noticeable, but for sure it wouldn't be a 100% match. I think for PVC or ABS bumper, it's completely up to you. ABS has a little more bend but if you try to do any repairs on it, it gets all fuzzy when sanding, where as PVC is easier to work with, but way more brittle. either choice, i recommend using a Plastic modifier
http://www.azautobodysupply.com/fusor-surface-modifier-603.htmlbefore priming and paint. less chance of peeling paint.