Spikecast
Super Freak
I'm not painter myself, but my Wolvie had a tiny paint chip in the blue shoulder area. So I just bought some blue acrylic paint to touch it up. Luckily mine had a damaged hand (one bent claw), so I was able to recieve a replacement. Although I smashed the original, I kept a larger peice so I could make sure the blue paint matched first beforehand.
You said yours was just a chip on the black part of the mask, that shouldn't be too tough. Just any black acrylic paint should do. Just make sure to use a tiny, tiny brush.
Thanks for the advice man. I'll get myself some paint They are replacing my EX head and the belt (scuffed) but it strikes me as odd they had no original heads left! Thankfully the chip is tiny so covering it myself won't be a problem. I'm not going to quibble when they gave me $25 back as well.