Clear anodizing, its actually really common, most people with aftermarket rims have it and just don't know it. Bare aluminum oxidizes. The way rim manufactures get around that (the good ones anyways) for their polished aluminum lips, is by clear anodizing them. Its not 100 percent clear, it leaves a sort of pearly tinge to them. Hard to describe.
Heres a good side by side comparsion pic I just snapped...
http://www.pbase.com/image/18631924
The rim on the left is clear anodized, the one on the right is bare polished aluminum. The bare one will eventually look like this...
http://www.pbase.com/image/15283141
once its put into use and left out in the elements for a few weeks or months.
If your aftermarket rims have "polished" lips and have never needed to be polished to restore their shine, then they are anodized clear. All of the Compomotives and original finish Enkies I've seen have it, its very common. You can actually wetsand it off too, not that you'd want to unless the rims are in really rough shape. Anyways, its fairly expensive to have done, costs a bit more then powder coating typiclly. Its also a little hard to find places that do it. Places that do gold plating, chroming and normal anodizing are your best bet. It aslo invloves alot of heat, so unless you have 3 piece rims and you take them apart, you have to strip off every bit of paint on your wheels before it can be done. It was suggested to me by Modern Autoplating (local company that does it) that powdercoating MAY survive the process, I've yet to test that theory. With powdercoating there is a special tape they have that can survive the heat and can be used to mask off surfaces. Say if someone was adventerous (and thrifty) they could have the black lines on the ptype wheels powder coated black, then clear anodize the rest. But a more econimcal way to go would be to have the whole wheel powder coated clear after the lines were done.