Case color is not "put on". It is a by product of case hardening steel. The parts are packed in charcoal and heated, then quenched. The trick is knowing the proper heat and time. There is always the danger that in the process, the metal can warp. There are several firms that are very good at doing this restoration. They can prep the metal for you.

Pete

http://www.damascus-barrels.com/Movie.html