Most of my life I've been a blonde man.  And women like Gretchen Moll, Elisha Cuthbert, Jennifer O'Dell, and Kate Hudson make me feel funny.  In that good way.
Lately I've noticed a strong attraction to Sela Ward, Claudia Black, Lauren Graham, and Catherine Zeta-Jones.  The woman I'm dating now is 1/2 Scottish,1/2 Mexican with raven black hair.  And my ex-wife had jet black hair.  Both are also older than I am (I'm 33).
So, in sum, I think that the 20-something betty needs to be blonde and the 35+ hottie should have black hair.  Which means, I guess, I prefere women with black hair since I've always been most attracted to women older than I am.