Some children start life as platinum blonds — often called "towheads" — but experience a darkening of hair color before they reach puberty. Just what causes this change in hue?
To begin: Your hair color is determined by the amount of natural pigment, called melanin, you have in your hair. Two distinct types of melanin exist — eumelanin and pheomelanin — and the ratio of these pigments guides hair color.
Eumelanin can be further broken up into two flavors: black and brown. Essentially, the more eumelanin you have in your hair, the darker it will be.