Shiva is depicted having blue skin color. Why is he not shown in normal human skin color? Hinduism is full of symbolisms and the blue color is also a symbol.
Blue is the color of the infinite. All Hindu gods are an attempt by the human mind to give form to the formless Brahman (The Supreme Truth or God in Hindu Religion). The color blue symbolizes immeasurable and all pervading reality – formless Brahman.
The blue color thus teaches us that what appears as Shiva is the all pervading reality. Brahman (the Supreme Reality) takes a particular form to satisfy the human mind.
Note – Shiva is also known as Neelakanda – one with blue throat. This is because when the ocean of milk was being churned by the Devas – (Demi gods) and Asuras (Demons) using Snake Vasuki as rope, the first thing to appear was a dark sticky foam. It was the dreaded poison Halahala, which had the power to destroy the universe.
Lord Shiva soon realized that the poison had the power to destroy the cosmos and immediately gathered the poisonous foam in his hands and drank it to save the world.
Goddess Parvathi, got alarmed about the safety of her husband Lord Shiva, caught hold of his neck to avoid poison from entering His body. The poison remained in the throat of Shiva making it blue colored.