5. In reality, the roundel is a tribute to both Rapp Motor and Bavaria
That blue and white? Those are the national colors of the German state of Bavaria, not white propellers on a blue sky or whatever you've heard. I'm not saying saying it doesn't look incredible when affixed to the nose cone of a propeller, but, again, that's pure marketing fantasy. Rapp Motor* was one of the key companies on which Bayerische Flugzeugwerke was founded and when BFW became BMW in 1917, the roundel was a natural combination of Rapp's logo and the Bavarian colors.
*Interesting side note: the founder of Rapp Motor, Karl Friedrich Rapp, left the company when it became BMW but stayed in Germany until 1934, when he suddenly realized that living out the rest of his days in Switzerland was a pretty good idea. Draw your own conclusions.