This seems to be consistent with my theory of hair as a frame. As facial features deteriorate with age (30), the absence-of-frame effect favors blondes at the expense of brunettes. At the even higher age (40) attractiveness overall declines and the absence-of-frame trick is no longer effective.
Percept Mot Skills. 2008 Jun;106(3):737-44.
Attractiveness of blonde women in evolutionary perspective: studies with two Polish samples.
Institute of Psychology, University of Wrocław, ul. J. Dawida 1, 50-527 Wrocław, Poland. firstname.lastname@example.org
An experimental study was undertaken to assess the phenomenon of male preference for blondes. In the first study, 360 Polish men ages 18 to 46 years were asked to assess the attractiveness of the presented stimuli using a 9-point scale. Stimuli were 9 different pictures of the same women whose ages (about 20, 30, and 40 years old) and hair colors (blonde, brown, and brunette) were manipulated. Pictures of blonde-haired women were generally rated as younger than the others. The attractiveness ratings of female faces changed with age and hair color. Still, only the 30-yr.-old woman with blonde hair was rated as significantly more attractive than those with brown or brunette hair. In a second study (the analysis of 500 Internet advertisements) mature women dyed their hair blonde more frequently. These results are analyzed with regard to the evolutionarily formed male preference for younger females.