On a whim and based on Darren Rovell's documentary on the with Sports Illustrated Swimsuit Issue, I did a quick scan on how the Dow and S&P performed in years that the magazine cover featured a blonde versus a brunette. I gauged hair color based on thumbnails on the SI Web site. Note: color of wet hair is hard to determine but here are the results...
>> Business Model: SI Swimsuit Issue
47 covers from 1964 until now: