He found that women with red hair were clearly more sexually active then those with other colors having more partners and more sex more often then the average, I guess the caricature of the fiery redhead certainly lives up to her reputation. He also found that women who changed their hair color to red were often trying to subconsciously signal that they are looking for a new partner. A psychologist involved in the study however stated another reason why redheads have exciting sex lives:

Red stands for passion and when a man sees a redhead he will think he is dealing with a woman who won’t mess around, and gets straight to the point when it comes to sex.