@SreeCharan There are many different stories to as to how Shiva's throat became blue, perhaps due to Kalpa Bheda. There's the story that he consumed the Kalahuta poison, there's the story that sage Narayana choked him, there's the story that Indra struck him with a Vajra, and there's the story that Sukracharya created snakes which bit him. But yes, the poison story is the most famous.