Blondes are more attractive than brunettes of redheads.
I am aware of the existence of Everyone Loves Blondes -- but that doesn't seem to be about blondes being more attractive, but rather about works containing a lot of blondes and averting other blondness tropes.dumb, evil, wholesome and lovely, and if a character has white hair, they're either very pretty or evil. Even when you're of a mature age, silvery hair clearly is The Way to be attractive. Whether it's platinum or dirty, golden or ashen, strawberry or honey, blondes are often considered superior in looks and attractiveness because of their hair. Want to be prettier? Bleach your hair. Who is the prettiest? The blonde of course. With men it tends to go the other way around -- black-haired men are preferable. See Tall Dark And Handsome. Blonde hair doesn't get associated with just purity, innocence, kindness and wholesome femininity -- blondes also have fame as being the pinnacle of sexiness, and even cruel and abusive sexiness. Appreciation of blondes is very much Truth In Television, and things like high interest towards blonde women in countries where black hair is predominant are widely known. The term "Swedish blonde" seems to be synonymous with "perfect woman". Of course, black, brown and red hair have their own fans. Light-coloured hair however seems the most appreciated.
Please only add examples where the superiority of blondness is more or less explicit in-universe. This is an ubiquitous, Truth In Television trope much like Buxom Is Better, and we don't want a laundry list of blondes in media.