Legend has that the evil king – Hiranyakashyap – forbade his son Prahlad from worshiping one of the Hindu gods – Lord Vishnu. However, Prahlad worshiped Vishnu despite his father’s denial.
Thus the demon king ordered Prahlad to sit on pyre (a structure, usually made of wood, for burning a body as part of a funeral rite or execution) along with Holika (who was immune to fire) the sister of the demon king. When the fire started, Holika was burnt to death in spite of her immunity to fire, and miraculously Prahlad was saved because Prahlad asked the help of Lord Vishnu during the event.
The burning of Holika is celebrated as Holi. However there are other arguments as well, that support the celebration of Holi and its origin. The story is also narrated in various ways but the conclusion remains the same i.e. – “victory of good over evil.”
Other legend behind the origin of Holi is that Lord Krishna as a baby was poisoned by the breast milk of Putana and thus he developed the characteristic blue color of his skin. Krishna was not sure if fair skinned Radha and other girls would like him. Thus he approached Radha and colored her face in some colors. Radha accepted Krishna despite the blue color of his skin and since that day the festival of Holi is celebrated.

Happy Holi!!!