Healthy hair has an intact cuticle which reflects light. Light also passes through the cuticle. At the same time, the pigment can be seen through the cuticle. The combination of this produces the colours tone.
Studies of hair pigment using electron and light microscopes, as well as chemical investigations show that there are two different types of pigment. In other words, there are two types of melanin. These two pigments produce the variety of natural hair colours we know.