Seems strange considering they've only been around since the '30s from what I understand.It was probably red lead to start with and became tradition.
If my memory is any good I believe it was Rod Stephens, Olin's younger brother, who invented them and the name came from the race boat they were installed on. She was named Dorade and built in the late 20's or early 30's.. Don't know why some are red, ours is white on the interior..Dorade vents are boxes that the turned trumpet style horns are mounted in. I believe that the ventilators are much older.