You are correct, the mat finish is without dye. For the various colors the anodized part is immersed in the dye color of choice then hot water to "seal" the surface. More trivia, the anodized surface, maybe .001", is harder/resistant to scratching (good for wear surfaces). The anodizing results in microscopic aluminum oxide "cells" which reduce the fatigue strength of the underlying aluminum so it's better not used on cyclically loaded parts.Oh yes that coloring (or lack of) is common with anodized aluminum. I'm not sure if they use a color to get it that way but my hunch is that's it's "natural". My ultralight airplane frame is all that same anodized finish.
Squirrell?! I mean - Airplane? Curious minds want to know more....
D