Try getting the receiver cleaned in an ultrasonic bath before you decide on whether to case colour.
Some of the results posted on this forum appear little short of magical.
That “magic” btw is, in my opinion, greatly exaggerated. First off…in order for the “magic” to happen the colors have to be present. Whether the colors are covered up from dried up oil, varnish or lacquer, they have to be there. An ultrasonic cleaner absolutely will NOT magically pull bright, vivid, case colors from metal that have been removed from handling, age, UV’s, etc.
What the ultrasonic will do is pull almost every bit of grease, grime, dirt, oil, and destroy any type of dried on goop etc out of every nook and cranny (including the engraving) on the action and parts.
Some ultrasonics are absolutely worthless (aka most Chinese pieces of junk). Their transducers being so weak they couldn’t even clean a piece of jewelry correctly let alone a gun with years of crap stuck to it.
Really good ultrasonics are not cheap either. A really good ultrasonic cleaner will clean so well, if there is any corrosion on the action or the parts, the cleaned corroded areas will show up as a dull spot. Those obviously need to be polished out to match up. Usually there’s some considerable time spent at the bench after the ultrasonic cleaning, polishing parts back to standard finish and so on.
They are neat, handy devices, but they aren’t capable of real magic.