Re: White Spiral on Me 109G Spinners
 

In the 1990s, the RAF took to painting stroboscopic patterns on the propeller blades of its surviving propellor-driven aircraft, and I can confirm its effectiveness. As these must have rotated at much the same speed as Luftwaffe fighters, perhaps a similar effect was still visible - though I agree that it could only have been of any significance at close ranges.

Similarly helicopter rotors have the top of one blade painted contrastingly to the others - although these will have slower rotation rates. In this case it seems exceedingly unlikely to be a ground safety reason.