Many years ago, in satya yuga, the sage Vashishtha met Kartikeya, the son of Shiva and Parvati. Having worshipped Kartikeya, the sage said, ―Please tell me how Shiva‘s throat came to be blue.‖ ―I do know the answer and I will satisfy your curiosity,‖ replied Kartikeya. ―I was once on Mount Kailasa, sleeping on my mother‘s lap. I heard my mother, Parvati, asked my father how his throat came to blue. And I will relate to you Shiva‘s reply. The gods and the demons once got together and decided to churn the ocean (samudra manthana). The gods and the demons were desirous of obtaining the amrita (a life-giving drink) that was expected to emerge as a result of the churning of the ocean. But when the churning began, some terrible poison came out and the gods and the demons were despondent at the sight of this poison, since they thought that it would destroy them all. They therefore fled to Brahma for protection.
―Why are you so despondent?‖ asked Brahma. ―A terrible poison named kalakuta has emerged as a result of the churning of the ocean; replied the gods and the demons. ―It is threatening to destroy the entire universe. It has even turned the great Vishnu‘s complexion black.‖ ―The only solution is to pray to Shiva,‖ said Brahma. ―He alone can deliver us from the effects of this terrible poison.‖ Brahma and the other gods started to pray to Shiva. Shiva was pleased at these prayers and appeared. He swallowed up the poison. But such was the strength of the poison that it made Shiva‘s throat blue. The word nila means blue and kantha means throat. Since Shiva became blue of throat, ever since that day, he has been known as Nilakantha.