I have seen it on an iPhone 5. Looked real smart. They had it done in a metallic burgundy. Spent over $300 with the shipping to have it done. So I can only imagine what it would cost for an Air. Looked great, but not sure I could justify the cost, unless I had money to burn.
Colorware is like a tattoo, can't undo. There are plenty of covers (temp tattoos) that will make your Mac looks different without commitment AND cheaper to boost. But hey if u got the dough and you REALLY like flat black go4rit.
All of the actual, non-"artist's rendering" photos i've seen of colorware hardware look pretty bad. It basically looks like they just painted a macbook with glittery spray paint. I think it would be great if Apple offered their computers in different colored annodized aluminum.