Melanin is the natural pigment that our skin makes.  The amount of melanin in your skin determines the color of your skin… from albino pure white (no pigment at all), to the darkest black skin.  The physiological purpose of melanin is to absorb sun light in order to protect the skin from sun damage.  Thus, the darker your skin is, the better your natural protection from sun damage is.  When skin is exposed to the sun, it produces extra melanin to protect against the increased level of sun exposure… otherwise known as a tan.