What is the relationship between the number of active genes and color of the skin

Skin color is polygenic trait meaning a lot of genes are significant in the expression of the trait. Such traits can have a multitude of variations showing continuous distribution because these non-epistatic genes have a cumulative effect on the skin color. The level of expression of these genes, majorly based on influence from the environment, will determine skin color. For example; the expression of the gene for melanin will be high in a person within the equator than in a person at the poles due to differences in sunlight exposure.