Most of the color variation is the result of the degree of polish given the metal. But that Colt Royal Blue was a proprietary process that AFAIK has never been duplicated by anyone else.
As to Carbonia blue, it is not a DIY process and not feasible for any home workshop or even gunsmith shop. Back in 2007 on this site I wrote:
"The way S&W did Carbonia bluing (note the "i") was to hang the guns in racks in a revolving drum in a gas furnace that was heated to over 600 degrees and had the Carbonia chemicals put in. The process was part of the heat treatment, which is why it could not be repeated. Guns sent to S&W for refinish were hot tank blued. If true Carbonia bluing is used by restorers, I would be somewhat concerned about refinishing guns using such a high temperature process, but I guess those guns will be for show, not use.
The guns were not buried in bone dust and there was no oil quench, just normal cooling; there was no mottling and no color other than the old S&W blue. Carbonia bluing is extremely durable and long lasting, not at all like heat bluing which is only a thin color on the surface. Like other finishes, the polishing has a lot to do with the final appearance, and can be anything from a shiny black to a "brush blue". (S&W's trademark hammer and trigger case coloring was done in a cyanide bath with air bubbling, not by any charcoal or bone process.)
Contrary to what has been written, Carbonia blue was not developed by S&W and was not proprietary. The process was developed by the American Gas Furnace Company, which rather gives an indication as to how it was used. Since it is a trademark for a specific process, not just a generic term for case hardening or bluing, I have capitalized it here."