Hey Sharabhi - I haven't refinished my calipers yet, but intend to at some point. Generally, you can either paint or powder coat. I've heard good things about Brightside Coatings locally, but have never used them. You'll find lots of shops if you Google it. Wheel Dynamics in California seem to do nice work, but expensive and far away.

A simpler, but less perfect solution is to reapply a new coat of clear yourself. It restores the gloss nicely for only a few bucks. Search the 993 forum for examples.

HTH!