The song "Neela Aasman" is actually based on a tune that Shammi Kapoor and Amitabh Bachchan composed together while shooting for Zameer (1975). During the making of Silsila (1981), Amitabh Bachchan called Shammi Kapoor to ask permission to use the tune. Shammi Kapoor had totally forgotten about it, and when reminded, he happily said: "Go ahead! Do whatever you want to with it!".
This was the last movie of Amitabh Bachchan and Rekha. Despite neither confirmed the rumoured link, they were never paired again and unlikely to feature together in the same movie.
Amitabh Bachchan was deeply involved with the music of this film. This resulted in the Holi song "Rang Barse", which was sung by Amitabh Bachchan and composed by his father Harivansh Rai Bachchan.
This is the only movie in which Shashi Kapoor is the Elder brother of Amitabh Bachchan. All their other movies in which they are brothers, Amitabh Bachchan is the elder one.
Amitabh Bachchan and Lata Mangeshkar recorded their portions of "Yeh Kahaan Aa Gaye Hum" separately. Years later, when they were on friendly terms, they expressed their regret at having to do so when they could have gotten to know each other.