Or even aluminum why not simply take it off, media blast it for a matte finish, and then get it anodised black?
Am I missing something? Is there anything inside it other that more aluminium?
That would be a simple and quick solution that would be relatively permanent (although it may go dark brown when it gets hot come to think of it, instead of staying black). That's still better than shiny silver.
Might cost you $10 to get it blasted at a local metal finishing place and $10-20 tops to make it black.