World War I was still being fought in Europe and it is possible (although unlikely) that this gun saw duty in the Great War (in case you slept through history class....the WWI ended on November 11th of 1918).
The 1911 pistols made after May of 1918 and before March of 1919 are often referred to as "Black Army" Colts. This was not a model designation, rather it was a reference to the darker appearing finish. In May of 1918 Colt began skipping the last polishing step in order to increase production during the war. About 325,000 Colt 1911s were made during this time.
Here are some examples of Black Army Colts, note the machined surfaces (lack of polishing)
For comparison, here is a 1914 production M1911, note the difference in the finish (also notice the change in the font.)
This Black Army 1911 shows how the finish did not age well on most of these guns. Prepping of the metal for bluing also saw some step skipping. According to my sources the guns were dipped in hot gasoline and then put into the bluing tanks, the gasoline left some residual oils which may have prevented an evenly blued surface.
Sometime during or just prior to WWII this gun was sent to the Rock Island Arsenal (this was the U.S. Army Arsenal in Illinois, not to be confused with the Rock Island Armory, a Filipino made 1911 copy or the Rock Island Auction Co., a private auction company) to be rebuilt which included the installation of a new slide.
We know this because of the RIA stamp under the serial number and the fact that the slide has the front 2 inches hardened. The hardening of the metal caused the darker color.
The U.S. Army (and Colt) started to perform this hardening on the slides in 1937 (under a new contract), this hardening was not present on the guns made before or during WWI.
The hardening process involved dipping the slides into molten lead and then quenching in oil.
This gun may very well have seen use in the second World War.....
Imagine.....(although not likely) this gun may have been to Europe twice to witness the defeat of the German Army!
Most of these guns, like this one, were refurbished during WWII, this was partly due to the poor finish applied (the final polishing was not the only corner that was cut).
These guns were given a phosphate "parkerized" finish during their time at the arsenals.
Here is how it would have looked when it left the Rock Island Arsenal, note the darker portion at the front of the slide and the parkerized finish.
To summarize, this gun originally was blued with an un-polished surface during WWI, then it was rebuilt with a new slide and parkerized during WWII. At some point after it left the service of the U.S. Army it was painted. The current care taker of the pistol removed the paint
Here are the pictures of this particular gun: