The whole range of natural colors of skin, eyes and hair, from burnt straw to raven’s wing, is due to melanin pigment.
Melanins (Greek: mhlas – black) are pigments that, in vertebrate animals, form in melanocytes – specialized cells of the skin, the iris of the eyes, and – what we mostly say today – hair follicles. Hair color (and skin too) depends on the amount of melanins, and on the ratio of their two forms – black-brown eumelanin and yellow-red pheomelanin, and on the size of their granules, and on the depth (the upper layers of the skin and the hair membrane are composed of colorless translucent cells), and from a heap of other hereditary factors about which science does not really know anything. Only general principles are known: in humans, dark hair is dominant in relation to light, and both are red. That is, if a fiery red blonde and a light blond blonde have a child with black hair, you have to recall the words of the famous Czech scientist B.S. Schweik: “Cross-crossing is generally a very interesting thing … Imagine such a scandal: you marry a young lady. White, scum, absolutely, and one fine day – here you are! – Negro gives birth to you. And if for nine months before she was once without you in a variety show and watched the fight with a Negro … ”
The name of the aforementioned comedy “Gentlemen prefer blondes” gentlemen immediately thought of a sequel: “… but marry brunettes, and sleep with redheads.” There is a share of joke here, of course, but there are not enough redheads at all: even in relatively blond countries, redheads (homozygous for a gene that is not exactly known to science) only make up about 2% of the population.