Its probably the least durable finish, and is sometime protected wih clearcoat.
The special edition reproduction models and the 36 is one come in the case color finish. Iread that it is done by Turnbull restorations dont know if its true, but they are highly regarded for producing authentic finishes.
They are also making a nickel 36 nickel is much more durable than case, blue is more durable than case color, but less than nickel.
IIRC the new 36 is like $800+
I have an old 36 I paid 1/4 the price of one of these new ones and I saw one for sale in a local gunshop , excellent condition blued, 1 7/8" barrel sq butt made in 1970 and they were asking $279.
So you can get the real thing for less than the reproduction if you look around. I carried mine in a pocket holster for 4 years and the blued finish held up better than thefinish on my current 642.