I think that hair-color descriptions refer to women unless otherwise specified for the same reason that Sarah Palin says that Hilary Clinton was treated unfairly when she ran for president. Women tend to be judged by and seen in relation to how they look--and that includes hair color. I don't always agree with Ms. Palin (now there is an understatement!!) but she nailed this one.
MACTECH ubi dolor ibi digitus