Someone correct me if I'm wrong, but I believe today at least, there are two different ways of coloring a receiver. One is "color case hardening", and the other is just " case coloring " . How the second is done, I'm not sure of. My friend uses bluing and browning solutions, bluing solutions cut in half with water, and so on. He doesn't clean the receiver, and dabs it on with his finger, wipes it dry when he gets the color he wants. Sometimes depending on the amount the steel is still hard he gets very good results. Other times not so. This I believe is not what I was trying to describe in the beginning.