In Sanatan Dharma, lord Shiva is the ultimate consciousness that is boundless and eternal, having no beginning or end. Lord Shiva first manifested himself through the cosmic roar, embodying his reality as lord Rudra, a fearsome form of Shiva.
To settle his anger, Shiva manifested his calm form, known as Shankara. It is the most peaceful and admired form of lord Shiva, known for living a yogic life on Mount Kailash.
In that way, Rudra and Shankara are both two different facets of physical Shiva. While Rudra is associated with eliminating darkness, and Shiva Shankara is the merciful Neelkantha.
Okay, let me share with you why lord Shiva is called by the name of Neelkantha.
Now you already know lord Shiva’s entire physical appearance is whitish. Only lord Shiva’s throat stands out with a beautiful blue hue. You must be thinking why lord Shiva’s throat is blue?
Here is your answer: Once upon a time, deities and asuras (demons) jointly churn the cosmic ocean to get precious materials. But before getting anything valuable from the churning, deadly poison came out of it. The poison was so lethal that it started destroying the world with its adverse effect. Immediately, everyone prayed to lord Shiva to save the world from the poison.
To protect the world from cosmic Halahal poison, Shiva bravely drank it. As a result, Shiva’s throat color turned into a gentle shade of blue. Because of his blue throat color, Shiva is called by the name of Neelkantha. Hence, blue color became an important part of lord Shiva’s look. This color is a part of the human chakras.