Russo, you are right about 610 for and after the American Freedom Train. Black boiler. Why, the rebuild and test run had to be completed by a certain date (can't remember the date) and they made it only by ONE DAY. No time to put green boiler and cylinder jacket on it. Then Southern leased it. When it came back no one wanted to spend the large sum to paint it "T&P". The whole thing had been done on a shoe string and if not for Amon Carter Jr even that would not have been done. All work done on it after it came back from the Southern was volunteer work. It basically had no place to run (it was fired up a few times at its storage place and run back and forth in the small yard).
A person who posts here, Tower Operator, also worked some on 610 and might be able to amplify on this.