Holi Anthem Rang Barse's Story And Unknown Facts

The song 'Rang Barse' from 'Silsila', featuring Amitabh Bachchan, Rekha, Jaya Bachchan, Sanjeev Kumar, is played every year on the festival of colours - Holi. What was the thought-process behind this song? What is the story behind it? Here is a video explaining all about it.