Newsflash, Colt used carbona bluing on all SAA's until WWII. Unless I'm mistaken, it was also present on all blued double actions. It was never exclusive to S&W.
Nope, not so.
During it's entire history, Colt used several different methods of bluing, but at any given time all models were blued using the method that was current for the time period, although some were more highly polished then others, and the degree of polish determined what the color would look like.
The earlist method was called
Charcoal Blue, which dated from the early precussion period to about 1919.
Carbona Blue was a similar process used by Smith & Wesson, as well as others, up through about 1940 or '41. Collt also used an alternative process called
Fire Blue to blue small parts, such as hammers, triggers, pins, screws, etc.
In or about 1919, Colt changed to a new finish, which was called
Gas Oven Blue, that continued until about 1941 when the factory was referbished for expected war production.
During the war, Colt switched to a bluing system that was, and still is, sold by the DuLite company. I believe they still use it today, although it may have been discontinued due to environmental issues. Colt's so called "Royal Blue" is based on this system. Post-World War Two SAA revolvers had (and I presume still do) have barrels, cylinders, back straps, trigger guards, and other small parts blued using the DuLite process.
Most of the pre-war Single Action's made between 1920 and 1941 (and a handful thereafter) had Charcoal Blued or Fire Blued parts made during earlier years, because by 1920 the demand for this model had substantually decreased.