Why is Krishna Coloured Blue?

One of the theories is that Vishnu, because of his association with water, is depicted blue; therefore all his incarnations, including Krishna, are shown as such. In Hinduism, persons who have depth of character and the capacity to fight evil are depicted as blue skinned. Another theory refers to Vishnu implanting two hairs, one black and the other whites in Devaki’s womb (which miraculously got transferred to Rohini’s) and as a result, from the black hair Krishna took birth, with a dark skin, and from the white hair his brother, Balarama.