The Colt New Service was the large frame double action revovler suited to the largest cartridges, .38-40, .44-40, .45 Colt, .455 etc. It was the largest and heaviest framed Colt until the Anaconda. It was the basis for the M1909 and M1917 Army revovlers, the Shooting Master and the New Service Target.
The Officers Model is a medium framed gun, limited to .38 Special and .41 Long Colt. It came from the Army And Navy Special and is the basis for the Official Police, the various Officers Models, and, ultimately, the Python.
Both of these guns in a 'Thirties issue and in good conditon, were the ultimate of Colt revolvers with beautiful blue finishes and smooth double actions even the Python didn't quite match.
The closest I can describe the finish of these guns is that it compares to the black Carrera glass once so popular in building construction.