Holi is a festival of colours, fun, happiness, love and devotion. In many ways, it is the battle of love. These colours represent love. To conquer each other with love is what Bhakti is all about. Holi also signifies the victory of good over evil.
The Holi festival is associated with the great devotee Prahlad. He was in the midst of the most gruesome situation we could imagine. But he was undisturbed and always blissful. This is because he revived his eternal relationship with the Supreme Lord through Bhakti Yog. He is always experiencing the unlimited love of Lord Narsimhadev. This loving relationship can alone bestow everlasting satisfaction and joy as stated in Bhagwad Gita 6.22.
The divine being the Supreme Controller protected Prahlad in all circumstances, even from being burnt in fire when Holika, who had the boon to enter fire unscathed, took Prahlad on her lap and sat in the fire intending to kill him on the instruction of her brother Hiranyakshyap. However, Prahlad was saved because of his extreme devotion for the divine, while Holika got burned. The tradition of Holika dahan, burning Holika, still continues.
We are living in a world plagued by lust, anger, greed, pride, illusion and envy. The solution: revive our devotion following Prahlad's footsteps. This way, we can celebrate every moment of Holi in our heart in any situation. This Holi of heart is the heart of Holi.