I had a post about a month ago asking about dying the white part of my headlight on my XR to match the black plastic on the bike now. Well, I ended up using black bumper paint. It's made to stick to plastic, and it's flexible. It cost about $10. That was for a can of primer, and a can of black paint. I don't have any major crashes on it yet, but I've gone through bushes and branches, and It's held up perfectly. DON"T us regular paints like Krylon. It won't last......
Hope this helps.
Jeremy