Highly likely Jews started spreading jokes about blondes among White people, right after National Socialist ideological portray of the blonde ubermensch. It's annoying when clueless Whites keep repeating these jokes about their own kind that are mindless.
It never worked. Even today brunettes are bleaching their hair.
I grew up with brown hair but in the summer it'd turn blonde in the sun. No bleach needed. Just go outdoors and enjoy the sun a little bit.