Shree Jagannatha puts on the Shraddha Besha in the month of Margasira (December) for three days during Dev Diwali. Shraddha means the offerings made out of love to dead ancestors and forefathers. Various rites, pujas and rituals observed for the departed souls (parents and forefathers) are called Shraddha.
In the month of Margasira, Shree Jagannath performs the Shraddha in favour of Nanda, Vasudeva and Dasaratha. We know that Bhagavan Vishnu was born as the eldest son of Dasharatha, the king of Ayodhya and was named Ramachandra. Again in the Dwapara Yuga, His birth took place as the son of Vasudeva in a prison in Mathura, whence he was mysteriously taken out and delivered to Nanda, the king of Braja, who nourished Him like his own son and came to be known as the second father of Bhagavan Sri Krishna.
In this Shraddha Besha, special rites are observed in the temple for three days. Bada Odia Matha is supplies the Shraddha materials to the Puri Jagannath temple as per tradition. The deities wear white clothes on this occasion.