I am going to go out on a limb and say that gun probably left the factory as a nickel gun just based on the blue extractor and the proud front sight pins. For whatever reason either the front sight itself and possibly the whole gun was refinished and the front sight became nickel.

At one time, if the factory did the nickel finish they did it in the style it would have shipped like originally (ie blue front sight, etc.). Our own 29-1 Chuck Odom has a 4" 5 screw nickel gun that shipped as blue but was factory refinished nickel in the proper style.

OP...look for the N as Doc pointed out, or take pictures of the sides of the grip frame.