I knew for years it was based on the national colours of Bavaria, but no... everybody had to parrot the airplane propeller myth. Just like those who call the cars "Beemers."
Then again, after WWII it was certainly in BMW's best interest to disassociate itself with the German war machine and Germany in general (of which Bavaria is a part - not to mention the home of the Nazi party). So... would you try to sell a car with German colours on it after the war (or let the propeller myth spread)?
Whoever put this together... thanks.