It's a Colt.
It has what looks like a fixed firing pin, but the retention pin is not in the USFA location.
It's in the Colt location for a fixed firing pin. Hole in the back edge of the hammer, correct?
It doesn't have a rampant Colt stamped on the left side, so not a 2nd gen Colt.
Spur is shaped like certain vintages of a Colt.