All Colt mags (all of which were made by USGI mag subcontractors, not by Colt) are finished in the standard molybdenum-based dry-film lubricant "finish", which is grey. The only exceptions were the mid-80's SP1s that came finished in "ColtGuard", and electroless nickel finish. ColtGuard SP1s shipped with two ColtGuard-finished 20-round mags.
The ONLY factory USGI-type mags that came in black were the teflon-finished mags made by La Belle. And none of these were issued to the military, as teflon, though a much better finish, was not Mil-Spec, and the teflon mags were made exclusively for civilian and LEO sales.
In the mid-to-late 90s, there were some fake "teflon Colt's" being sold at gunshows. Someone had simply taken new Colt mags and applied a bake-on Teflon finish *right over the top of the moly dry-film*. Of course, this meant that the teflon made the mags too thick, and the teflon scraped off pretty easy. And the mag vendors made up some great stories about these mags being "issued to the Navy SEALs!" and "ultra-rare, and worth much more than the $60 each that I'm asking!"
If you believe that one, I could give you a really good deal on a slightly-used B2 bomber...