It's difficult to show & explain online.
In person handing you 2 guns would be much easier to show.
Colt standard Blue would look something like this...
The Colt Royal Blue will look almost like it's still wet it's so shiney and the finish looks very deep. It will look so dark & wet it looks black. It's all in the gun prep before the gun is Blued. Like this...
I wouldn't go by the Blue Book mention of "Blue or Royal Blue".
There was no "standard blue" Python and another series with "Royal Blue".
You'll notice there's NO PRICING difference listed.
From 1955 up through the 1960's the Python was better polished, with that deep, glossy "Royal Blue" finish.
After the 60's, GRADUALLY the quality of finish deteriorated slightly.
The Python still had the best bluing of any production gun, but it wasn't up to the standards of the early models.
In other words, there was no "break point" where Python 12345 had the Royal Blue and Python 12346 had a lesser finish.
Inside Colt, the Python blue job was always known as "The Python finish, not as Royal Blue.
Colt didn't even use the Royal Blue label in advertising all the time. It was used on and off for a number of years and for various guns.
Due to the presence of the undiluted bright blue Python finish on the 50's and 60's Pythons, this is one major reason the early guns bring more money, but there is no point at which you can say these were Royal Blue, and these are just blue.