Pavitra baras is a special ritual observed by Vaishnava sect of Hindus. In 2016, Pavitra Baras date is August 15. It is observed on Shukla Paksha Dwadasi in Shravan Month.
On this day, Lord Sri Krishna or Vishnu is worshipped by offering Pavitra (cotton threads). It is widely observed ritual in Gujarat, some places of Maharashtra, and other North Indian states.
The similar ritual is observed in Andhra Pradesh and Karnataka as Pavitrotsavam (Pavitrotsavam is a famous ritual in Tirumala Tirupati Venkateswara Temple).
As per ancient Hindu texts, there are different bhavas of Pavitra. Kesri coloured Pavitra represents satvik bhava, white and red represents rajas bhava, green coloured is tamas bhava and sky blue is nirguna bhava.