Ever wondered why people have different colour hair? Hair colour is the pigmentation of hair follicles due to two types of melanin: eumelanin and pheomelanin. If more eumelanin is present, the darker your hair. If less eumelanin is present, the lighter your hair. The change in level of melanin can cause a person hair colour to change over time.
Here is a study by Indiana University showing the inheritance of brown hair.