Moles are generally black or dark brown in colour. They may darken and become black due to exposure to the sun, during pregnancy or during ones teen years. Moles are caused when cells within the skin are clustered or closely concentrated rather than being spread out normally. These cells are melanocytes and irt is these cells that lend natural colour to skin. It is believed that ultraviolet light can cause changes in the colour of moles. The scientific name of a mole is melanocytic naevus. It is a type of skin lesion known as naevi. People with moles are advised to monitor and keep a check on their moles as changes to the moles can be a sign of cancer developing. Moles are also considered beauty spots by many.