I can't speak to all guns at all times, but in my collection (Target---begining to end) the 19th century products were "Bright Blue" (high polish)----or nickel---on into the early 20th century. In the 1920's-early 30's, the matte blue appears to have become the standard (blue) finish---"Bright Blue" available on order. Beginning in the late 30's, "Bright Blue" seemingly became the norm. Immediate post WWII products were matte blue (to speed things up, as noted earlier) with "Bright Blue" again available as special order. From that point into the early-mid 50's such a special order usually took six months---and didn't get a lot of takers. I know little to nothing about products after the late 50's.
Note was made of "hand polishing". S&W products were polished with formed leather wheels (at least up to the point of moving from old factory to new factory (mid-50's)---and likely beyond. (??) (If it ain't broke, don't fix it!). They had/have(??) about a gazillion of them to fit all the myriad surfaces on all the products. The knowledge/skill required to polish was knowing which wheel to use for which surface, which compound to use for which finish, and how hard to lean on the work---and especially how hard not to lean on it. I suspect, (and will bet money on it) the only hand polishing was done to blend/correct minor boo-boo's----some of which were missed. (I have a late 30's M&P in "Bright Blue" that will bring tears to your eyes. The gun is as new. The finish (the polish actually) is the most atrocious, sloppiest work you have ever seen----every place it has a place. I figure it was done late Friday before a hot date or early Monday after a particularly punishing weekend. And I figure both the polisher and the inspector were related.)
Ralph Tremaine
And as noted earlier, some guns were always "Bright Blue". In the target world, 1st and 2nd Model Single Shots were either "Bright Blue"------ or nickel. 3rd Model Single Shots were both "Bright Blue" and matte blue---seems like the early 3rd's were the "Bright Blue". All the Straight Lines were "Bright Blue".