I saw a tip in a mag that says ;-gently heat the plastics with a heat gun,of course being ultra carefull!
I did some plastics that i got from a scrappy on sunday.They had what looked like a paint on which i had to remove with stripper,before i used black shoe polish.
The back to black 'temp' effect can be acheived by using wd40 or the one of the same.-and MUCH CHEAPER .