The wreck that Patrol A1 found was not painted at all and if it was the B-17, you are then saying the paint was gone after two and a half years ?
Some B-17 cowls were painted. Some were not. Some were half painted.
We have no way of knowing whether the engine/cowl was found upright or inverted. From the sketch, made many many decades later, very little of the cowl remained.
An absence of memory of paint is as uninformative as a memory of absence of paint in this case. It's a B-17 part in a known debris field of a (now) known B-17 crash debris field.
Sure, the guys were unaware of the B-17 crash. Sure, the guys hoped they'd found Amelia Earhart. So the legend was born. Legends like that die hard, especially when people truly madly deeply want to believe the legend.