Howdy
This is a photo of the Case Hardening on one of my Colts. This is a 2nd Gen Colt made in 1973. I have put a great deal of Black Powder through this pistol over the years, and do not always clean it as soon as I should. Consequently, the colors have faded a bit.
The next photo is the Case Hardening on the frame of a Cimarron Cattleman of mine. I have not shot this pistol as much as the Colt, and the colors have not faded as much. But they were never very strong to begin with. Notice the hammer has also been Case Hardened on the Cattleman, but not on the Colt. Colt does not currently case harden hammers.
Just so you know what a fantastic Case Hardening job looks like, here is one of Doug Turnbull's masterpieces.
Here is the fake Color Case finish on an 'original model' Vaquero of mine. This one has not seen as much Black Powder as my Colt, so the colors have not faded much. I know many folks have reported problems with the fake Ruger colors, which is why Ruger discontinued them a year or so ago. But I have had no such problems.
Lastly, here is the fake Color Case finish on a New Vaquero of mine. Again, I have had no problems with it or its twin.
Now, aside from the spectacular colors that Turnbull achieves, notice how much 'blotchier' the Ruger fake colors are than the true Case Hardening colors of the other three revolvers. Notice how much more subtly the colors blend together with the real thing. Actually, my New Vaqueros have a pretty good imitation of real case colors, not too bad at all. But the other Vaq is pretty blotchy.
It is true, the colors on real Case Hardening can fade over time, and with exposure to harsh chemicals. Even strong sunlight can fade them. Turnbull coats his guns with a clear lacquer to protect the colors. But even if the colors fade, the thin hard skin is still present with real Case Hardening, doing its job of reducing wear. That is what Case Hardening was invented for in the first place, to harden the surface of the metal. This was before modern steel alloys existed that could be heat treated to harden them completely through the metal, which is by the way what Ruger does and why the colors are fake. The metal is already hard all the way through. Nineteenth Century gun manufacturers originally were just trying to harden the surface of the steel, the colors were just a by product of the process. But eventually, they realized the colors were a selling point all by themselves, so each manufacturer developed their own process to maximize the colors. They all jealously guarded their processes. Turnbull has managed to recreate these processes.
And yes, neither real nor fake Case Hardening will protect against rust. The steel is raw, there is no coating to protect against rust as there is with blued steel. Raw steel must be kept oiled, or it will rust.