Gil - Case hardening and the coloring associated are two different processes, as I understand it. You can case harden without a trace of color and you can color without hardening; the fact that are often combined has lead to the belief that they are one and the same process. The trick going on here seems to be that some of the better technicians are using the lower temperature coloring process without affecting the hardness. If you are familiar with tempering colors, you will know that color forms on polished steel at temperatures way below the critical temperature. So, in theory, color can be restablished without warpage, shrinkage or softening of the reciever.
If I understood OG correctly, he recommended quenching from a temperature just low enough to avoid martensitic formation; he was trading some hardness for dimensional stability. The case he recommended was much harder than low carbon steel surfaces, but not as hard as a martensitic surface. In gun service conditions, this was a very good trade.
