Hair color is determined by genetics that affect how much eumelanin and pheomelanin pigments are in your hair. The more eumelanin genes there are, the darker your hair will be. So, a little eumelanin and you are a blonde, a lot and you have black hair. Pheomelanin determines how red your hair is. A little eumelanin and a little pheomelanin will produce a strawberry blonde. More of each result in auburn hair. Just a little eumelanin with a lot of pheomelanin results in a fiery redhead.