if you polish the metal, with the finish removed and metal in the white. you can play the surface with a acetylene torch with a small tip and a carburizing flame, this will change the surface color of the steel, with some practice you can get a close approximation of case colors. We were taught to do this, usually on older single shot shotgun receivers made of questionable alloy that would not take bluing. It does not take much heat to change the color. It would be a good idea to practice on some scrap steel to get a feel for it, before you go to town on your parts. It is not very durable but it does work