Redheads are a natural turn on and long, nice brown hair is usually attractive. Blondes can be sexy, but not the first tendency for someone I would date. Black hair is probably my least favorite unless you have darker skin tones.
I do not have a preference. Seriously, I find many hair colors beautiful, just beautiful in different ways. The only hair color that turns me off is really obnoxious teals or unnatural tints that made it look like a girl dumped a bucket of paint on her head. All other natural colors and highlights that are spin offs of naturals are just fine in my book.
Anything, the crazier and more different the better I say, but I have to put blond at the bottom, it can be combined with other colors to look great, but I generally don't like it as a stand alone color of hair.