Would you not date a person strictly for their hair color?
There are many reasons to date a person, and many factors that apply to a relationship and it takes more than simply hair color to make a relationship work.
While people always have preferences for hair color and eye color, those superficial characteristics are not why a person dates another person. Justin bieber doesn't care about the color of people's hair; as long as they're cute and funny, the hair color doesn't matter. He will go out with anyone -- any hair color and any height because neither really matters!