You know what I realized while watching Brave for the 5th time this month, it would be more likely that Merida's hair color would be brown (like her mothers) than red. Brown hair is a more dominate trait than red, but it would be possible for her hair to be red if her mother had a red gene in her and the family line aka recessive gene. On the other hand her brothers have it too, all three of them which means that for their family, the red hair gene is dominate while the brown hair gene is recessive.
It seems to make sense, but either way I still love the movie. Won't be able to watch it the same way because I have analyzed it too much for my class.