Ds isn't a redhead but his hair is getting super light since both DH and I have dark dark brown hair. DS still doesn't have eyebrows :(.
But Dh's mothers side of the family are all blonde haired and my mom was a toe-head until she was 4, so that's where I'm thinking the lighter hair comes from. Dh also pulls a reddish tone in the summer and in his beard when the light hits it right.
My friends daughter is carrot top red head, the mother has dark brown hair and father has blonde hair.