It seems to me that they are so finely / closely fitted, that getting any kind of coated or plated finish on the disassembled parts would make it awfully difficult to reassemble in the same nicely fitted fashion.
I have seen photos several years ago on one of the gun forums of a FA 83 that had been given a Desert Camo finish on most of the gun.
As I recall the cylinder was not coated. Peoples tastes vary, obviously, and what one does with their gun is fine with me, but that one left me almost speechless.
To answer the earlier question, "No", stainless steel can't be blued or CCH in the conventional fashion, and I've never personally seen a coated finish that was as fine as good bluing or an FA stainless finish.
If it's got to be blue, I believe you'll have to have one of the finest craftsmen build a Ruger.