With WWI in full fury Colt was instructed to speed up production, and cutting corners on the finish was probably the easiest thing to do to cut down on production time and increase output. The final polish was not as good as previous pistols, and the blueing was sub-standard for Colt. The rough polish and sub-standard blueing gave the pistols a darker finish, and from being described as having a black finish morphed into "Black Army" as if it was another model altogether. The finish did not adhere to the pistols well, and today WWI vintage 1911's with a high percentage of finish are scarce. It became so important to have a "Black Army" that inquiries were made of no finish and refinished pistols as to whether they were a Black Army or not.
The term applied to Lugers with black plastic grips was "Black Widow". Ralph Shattuck takes credit for coining the term. Ralph has been a dealer for as long as I can remember, and the Lugers with black plastic grips did not sell well. As soon as "Black Widow Luger" showed on on the market, everyone had to have one. Now 1911 collectors must have a "Black Army", although as mentioned above, 1911's with an excellent black finish are scarce.