The common wisdom is brush-painted red, and that is what the Concours Committee expects to see on cars submitted for judging.
However, in those olden days of iffy standardization, multiple simultaneous union strikes, and occasional shortages of supplies, it is quite possible that some slipped through within the red paint. I would hardly think that they would hold up a car on the production line waiting for a striking fan shroud painter to come back to work.
The rule? Red. The exception? Sure.