FWIW, the anodize on aluminum can be any color at all. Or, more correctly, the anodize coating itself (which is simply a very thick, relatively speaking, induced oxide coat similar to what forms naturally to make aluminum corrosion resistant) is colorless, but at one point in the process is porous and can be made to take up any dye desired, before the pores are sealed over. I've seen anodize that was bright red, bright yellow, bright green, dead black, and a number of sublter shades, as well as clear or very nearly clear.

Anodize really amounts to mounting your print on sapphire -- but be aware what the dye that colors an anodize coating might do relative to archival standards; not only can the dye in anodize fade with light exposure (like any dye), there's a question in my mind of what the dye decomposition products might do to your print. If no dye is used, this won't be an issue (and the acid from the anodize is washed out in the finishing process), but then you'll have a surface that looks like aluminum or like aluminum with a translucent white coating.

I've also seen examples of people applying a silver halide sensitizer to porous anodize, exposing, developing, fixing, washing, and then sealing the anodize to trap the image within the aluminum oxide coating. Now *there's* an archival substrate...