Are you sure the B-17 was painted the way it was when it was built? Most that I've seen have pin-up girls painted on the nose, and have been given a name of some kind, and they have bombs painted next to the cockpit,as if they had actually seen combat, which none of them have. But the people want, and are willing to pay to see "real warbirds." The exception of course is Memphis Belle, which isn't flying, but has seen combat.
In addition, federal regulations require that they have a N-number (registration number) painted somewhere near the tail. (It's usually under the horizontal stabilizer, so it isn't too obvious.) In order to fly them, they are registered as "experimental". This requires that the word "experimental" be posted somewhere near the doors.