Aluminum is usually colored by anodization. It's a great looking finish, and fairly tough too. Though it could be a bit costly to do for just a couple small parts. Probably check local chroming and electroplating shops; if they can't do it, they can probably point you to somebody who can, or at least for an estimate. Some anodized parts on a camera would probably look really sharp though.

Another thought I had is parkerization. My dad refinishes WWII-era guns, and uses a home parkerization kit to do some of the smaller pieces. It's a flat (as in not glossy) coating, and it's pretty tough. I'm pretty sure it's an electroplating process. Though most of the gun parts my dad deals with are ferrous metals, so I've got no idea if it'll work on aluminum.

Will