Someone here recently suggested rubbing raw onion over a polished receiver to tone it down and age it. I have not tried it.
I recently picked up a 12 ga. field grade L.C. Smith quite reasonably, but it's frame has been blued. I intend to strip the blue and probably leave it silver, or try the onion trick. It, like many lower grade guns in average condition, would be hard to justify spending $2-300.00 on new case colors. The case hardening is still there. Only the colors are gone.
If someone named Ed should suggest torch coloring your gun, politely laugh your ass off. Then decline.
