In my opinion the first requisite is that they are willing.
The second is that they don't take one look at me and either burst out laughing or say "You must be joking".
Over the years I have enjoyed the company of blondes (Natural and Bottled), brunettes and the odd redhead.
One memorable GF was Eurasian with naturally jet black hair. Father was Dutch and Mother was Chinese (Hong Kong type).
Frankly I have no preference. If they like me and I like them hair colour never enters the equation.
Oh and it helps a lot if they stutter over the word NO! 
I don't like freckles much, though a light dusting over the nose can look cute.
It sounds like you will be ticking the 'anything with a pulse' box 
If it helps I have only ever married (or been engaged to marry) Brunettes.
Is a pulse necessary? Warm would do ......
