www.essentialarms.comYou could have guessed that one. This is the cheapest lower on the market, and despite being cast, work well. Have never seen one break. The machining, fit of the parts, is precise. You can get them in the old gray color or a black coating.
My last four builds have been on DPMS lowers. They fit and match color on most all upper receivers.
You can't buy an Armalite stripped lower, unless someone disassembled an Armalite and sold the lower. You can buy an Eagle Arms lower (made by Armalite). They reserve the Armalite name for factory built Armalites. The Eagle Arms lower is identical but for the name.
Double Star, Rock River, Stag, LAR, PWA, and others are also good lowers.
As far as colors, they are all going to be black. You can have them coated another color. I did a few with Norrell's Moly Resin OD. Armalite now markets the synthetic lower made by Cavalry Arms. They are stamped Eagle Arms. These lowers are an excellent value.