Colt never offered "fire bluing" on the Python.
The early Python's extraordinary blue finish was strictly the result of hand polishing by a Master polisher, with years on the job.
Colt always made their own wooden, leather covered polishing wheels, and when other makers guns were being blued, the Python was still being polished with finer and finer grit media.
Colt's final polish on the Python was with a media that had the consistancy of flour.
That's why the early guns have that super glossy, mirror-like SHINE to them.
They were just polished more.
The Pythons made in the 50's and 60's were polished better than later guns.
The cost of all that hand labor for the mirror-like blue was simply getting too expensive by the 70's, and Colt was faced with the choice of huge price increases, or cut the level of polishing "slightly" and hold the line as much as possible on price.
Even with the reduction in polish, the Python still had a better polish and blue than any other production revolver.
The difference is hard to explain, and no picture can capture the difference.
You have to see an early Python, and once you have, all other blue jobs look dull by comparison.
Over the years owners and factory advertising have used various terms for that blue.
Royal Blue, Midnight Blue, Ultimate Blue, and others have been used.
Inside the factory, that blue was and still is known as "The Python Blue".
The actual chemical process used is the same hot salts system as used by all modern gun makers.
The only difference between Ruger's somewhat flat black, and the Python's glossy blue is the polishing done before the actual bluing.