The Company did supply all blue, pinned, unmarked mags with with pistols during that time. It also supplied two-tone, pinned and unmarked ones through 1913 & 1914. These magazines started out as all blue, pinned & unmarked, but were subjected to the improved hardening process that resulted in the two-tone appearance The next new batch of magazines were crimped base, and have the typical appearance of two-tone, round top, marked variety.
Colt was always mindful of the bottom line, and would never allow perfectly good parts to go unused. They simply would 'build out' the excess old stock and continue forward. This would explain the seemingly random distribution of features, updates, and modifications among many product lines, and complicates the authentication process for a lot of guns. To further scramble the timeline of production runs and shipping history, there were many guns shipped out of numerical sequence, depending on how and when the product was drawn from stock. Combine these circumstances with random modifications & updates and you will encounter conditions that are not logical.
So...either type of magazine is correct for that pistol.
I like the two-tone, pinned & unmarked theory. I know such magazines exist.
If this isn't confusing enough, check out the deal with the thumb safety on the model M.
That is another case where pistols appear to have features that they either shouldn't, or have been modified post-factory, or came through production out of sequence.
Part of the appeal of Colts is the head-scratching that one must do to figure things out.