Right, and it's that controlled, even, and thick layer that you don't necessarily get from exposed aluminum. Check an old aluminum ladder, they often get rather crusty and pitted.
Likewise browning is controlled rust, but if you just strip the bluing off a gun and let it sit you don't get the same effect at all
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Rust, iron oxide, is weak and friable, though, unlike aluminum oxide.
Looks like OP might be able to chemically strip just the color: http://www.instructables.com/id/Removing-Anodizing-From-Aluminum-Quickly-and-Easil/