A recent HBR.org newsletter factoid points to a Queensland University of Technology study showing that blondes earn 7% more than brunettes. This effect "is as large as the wage boost from an additional year of education," according to a study of 13,000 caucasian women.
This blonde effect has coattails. "The men they marry earn an average of 6% more than husbands of women with other hair colors," according to the research authored by David W. Johnston.
This data courtesy The Daily Stat newsletter from Harvard Business Review.