There are no bare aluminum USGI mags.
The gold you're seeing is a dye that is added to the hard-coat anodizing process. HCA'ing aluminum gives it a very thin, but very hard surface finish that protects the softer aluminum underneath. If you've seen aftermarket "racing" hoses for cars, the connectors are often anodized red, blue, or "clear" (silver).
USGI mags have been anodized in the following colors:
The color isn't significant; it's just the color of the dye they happened to use. One isn't any better than other, except asthetically.
USGI mags have a molybdenum-based dry-film lubricant applied to them as a "finish."