Blue eyes contain low amounts of melanin within the iris stroma; longer wavelengths of light tend to be absorbed by the underlying iris pigment epithelium, and shorter wavelengths are reflected and undergo Rayleigh scattering. The type of melanin present is eumelanin. The outer surface of the iris of a blue-eyed person is clear, lacking the outer layer of pigmentation that is found in brown eyes. Their color is caused by the inner layer of pigmentation and the semi-opaque fibrous tissues that lie between the two layers.
Brown hair is the most common in Europe. It is characterized by higher levels of eumelanin and lower levels of pheomelanin. Of the two types of eumelanin (black and brown), brown-haired people have brown eumelanin; they also usually have medium-thick strands of hair. Brown-haired people are often known as brunettes/brunets.
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