The dark coloration of the cells in the substantia nigra (literally “black substance”), the structure in the brain that regulates motor function. A chemical called melanin, the same substance responsible for skin color, causes the coloration. However, there is no correlation between skin color and the amount of melanin in the substantia nigra. Scientists do not know why these cells deep within the brain contain melanin; there does not seem to be a functional purpose. Melanin in the skin helps to protect the skin from ultraviolet radiation damage that results from Sun exposure; it is what causes light-colored skin to “tan.” There does not appear to be any connection between melanin and Parkinson’s disease.