depends on what you mean by favorite color... on who?
i don't have a preference one way or the other with the guys (or the previous occasional girls) i've been with. (ignore the bomb i just dropped please) i seem to gravitate a bit more towards lighter hair. i prefer easy-going people and seem to find this more in lighter hair. <shrugs>
my own hair has been more colors than i can remember but it always seems to end up blonde again. my natural color is an auburn/light brown (i think, i don't remember
) and it's heavily highlighted blonde. i get many compliments on my hair and honestly i think people seem to look my way more when it's blonde. that almost inspires me to darken it (as i am rather social phobic and hate people as a general rule)
it seems people with darker hair are taken more seriously. perhaps for this reason i like my lighter hair
life's too short to be too serious. 
i don't have a preference one way or the other with the guys (or the previous occasional girls) i've been with. (ignore the bomb i just dropped please) i seem to gravitate a bit more towards lighter hair. i prefer easy-going people and seem to find this more in lighter hair. <shrugs>
my own hair has been more colors than i can remember but it always seems to end up blonde again. my natural color is an auburn/light brown (i think, i don't remember
it seems people with darker hair are taken more seriously. perhaps for this reason i like my lighter hair