I have a barrel marked "Colt 45 Auto" at the 7 o'clock position on the left side, "P" on the left lug and a "F" on the underside of the barrel just forward on the lugs. I think it goes in the Colt S/N range 712350 to 2 Million. But the color is grey/green parkerizing. Is there such an animal or has been Bubbarized?

Original finish military barrels are blue.

Barrels taken out of pistols during rebuild that were serviceable were sandblasted and given a phosphate finish, and reused. The F mark ahead of the barrel lug came into use in the late 1943 time period around serial number 1,100,000.

Thanks Johnny, That solves my problem. The bore of this barrel is almost new.