Comment by numpad0

You have to grind off the existing Al2O3 protective layer using sandpapers/sandblasters and/or power tools, then ultrasound + acetone wash the parts, then dump it into an acid bath while running electrical current through the pieces. Special dyes can be added for color. Then the pieces are boiled in regular water to further improve durability. The combination of the acid and electricity then boiling cause Al to form beehive shaped surface micropores, and dyes - actually inorganic, so pigments - gets electrically jammed into the pores. The whole outer surface become thick insulating layer of highly chemically resistant and mechanically rigid white/transparent Al2O3 once the process is complete. Voltage, current, waveform, temperature, solution acidity, etc etc affect colors and oxide thickness and shapes and sizes therefore aesthetics as well as durability. "Anodization" refers to this process of electro-acidic-heat formation of the oxide layer, not the coloring. The coloring powder is an extra.

Technically it can be done in a garage, but spot and/or intact application might be difficult. Strict color matching against Apple made things would be impossible.