Colt Royal Blue is not a process like Carbona, it's a standard hot salts blue that's done after the metal is given the finest possible polish job.
Royal Blue was known inside the Colt plant as "the Python finish" because that's the first gun it was used on.
The only difference between Royal Blue and the bluing done on a standard Colt like the Detective Special is that the Royal Blue is polished to an extremely fine finish by a master polisher using very large, very hard polishing wheels.
There was an old saying that while other makers guns were being shipped to the distributor, the Python was still in the plant being polished.
Colt still does the Royal Blue, and they refinish guns to like new appearance.
If all you want is one slide re-finished, by far the cheapest way to get it done is to send it to Colt.