It strikes me as unlikely anyone at Colt mistakenly Parkerized barrels. Barrels and magazines were always blued. Just because I run onto phosphate finished magazines now and then, I don't believe they came new from the factory that way.
As I stated before, it will be almost impossible to ever establish a credible base of evidence because there are so many refinished barrels in pistols and so many people who don't really know enough to determine if they have an original barrel in a pistol. And I'm sure there are a lot of people with phosphate barrels who'd like to think their pistols are original.