SB 4.14.45
tam tu te ’vanatam dinam
kim karomiti vadinam
nisidety abruvams tata
sa nisadas tato ’bhavat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
He was very submissive and meek, and immediately after his birth he bowed down and inquired, “Sirs, what shall I do?” The great sages replied, “Please sit down [nisida].” Thus Nisada, the father of the Naisada race, was born.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
It is said in the sastras that the head of the body represents the brahmanas, the arms represent the ksatriyas, the abdomen represents the vaisyas, and the legs, beginning with the thighs, represent the sudras. The sudras are sometimes called black, or krsna. The brahmanas are called sukla, or white, and the ksatriyas and the vaisyas are a mixture of black and white. However, those who are extraordinarily white are said to have skin produced out of white leprosy. It may be concluded that white or a golden hue is the color of the higher caste, and black is the complexion of the sudras.