I can't quantify an Irish preference for dark hair among women but a common poetic name for Ireland is
"An Róisín Dubh" - The Black Rose - a beatiful black haired woman. The "Cáilín Dubh" - black haired
girl - is prominent in Irish literature as an object of desire. Yet, the Irish "Buachaillín Bán" - fair-haired
boy implies a favorite son.