Just find a place closest to you that anodizes aluminum. When I made some parts for a company out of aluminum, I had to anodize them for added strength. Black was the chosen color and it came out nice. You just see marks on it a whole lot easier. From basic stuff like having your hands on it to the tiniest of scratches.
I think apple does anodize their aluminum products, just a clear anodize. If people want their unibody macbooks and macbook pros anodized a color of their choice, just take apart the laptop and get the shell done. Depending on how precise the tolerances are for the screws will determine how easy it is to screw back together. Anodizing isn't very thick, so it may just provide a tighter fit for some things when piecing back together.