It's a white flight cap, the guy is Erwin Fischer, 1./Fernaufklärungs-Gruppe 121 ..
Here few small pics where you can see it compared to a white visor cap.
I've seen inflatable swimmingvest in a very light color, so in a pic they will look like white.
This guy operated in a glass cockpit in tropical areas I believe, so the white color was probably to reflect sun light to reduce the heat, just my guess.
Nevertheless a very interesting cap.
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