Skin color is inherited through multiple genes. This is called “polygenic inheritance”. Traits inherited in this way have many possible outcomes that are determined by interactions among several gene pairs. A gene is a pair of “alleles”, the pair can either be one dominate and one recessive that results in the dominate trait outcome, two dominate that also results in the dominate trait, or two recessive that results in the recessive trait. Typically, dark is the dominant trait. Examples of polygenic inheritance in humans include traits such as skin color, eye color, hair color, body shape, height, and weight. Most individuals inherit various combinations of dominant and recessive gene pairs (alleles). This results in a wide range of outcomes typically described as a distribution. Eye color inheritance is influenced by up to 16 different genes. It is determined by the amount of the brown color pigment melanin that a person has in the front part of the iris. Black and dark brown eyes have more melanin than hazel or green eyes. Blue eyes have no melanin in the iris. Several other genes that determine eye color also influence skin color and hair color. Skin color is determined by at least three genes and other genes are also thought to influence skin color (the exact number is still unknown). Skin color is determined by the amount of the dark color pigment melanin in the skin. If we consider only the three genes that are known to influence skin color, each gene pair has one allele possibility for dark skin color and one for light skin color. The allele for dark skin color is dominant to the allele for light skin color. Skin color is determined by the number of dark alleles a person has. Individuals who inherit no dark alleles will have very light skin color, while those that inherit only dark alleles will have very dark skin color. Individuals who inherit different combinations of light and dark gene pairings will have various skin shades. Those who inherit an even number of dark and light alleles will have a medium skin color. The more dark alleles inherited, the darker the skin color.

Source:
• http://ghr.nlm.nih.gov