There are several variations of late war shell casings. The steel casings were Parkerized to prevent them from rusting and to keep them from sticking to the insides of the breech after firing. The common color of this Parkerization, (at least in the images I have), is a light yellow-green, sort of a "Key-Lime Pie" color, for lack of a better term, although there were apparently other colors as well. There were also brass and copper plated rounds, which were made of steel, but covered with a thin electroplated coating of brass or copper.