Why are porn movies called blue film?

There are many different theories about why they are called "Blue" films, but no one is really certain about why they are called blue. 

• One theory is that the term came to be in use from the fact that in the 1980's, pornographic content in video cassettes was sealed using a blue tape.

• Another theory suggests that it started with the blue bars across the faces of the actors or actresses to obscure their identities. And since striptease acts might have used blue spotlights, this might also have been the origin of the blue in blue film.

• Yet another theory attributes it to the bluish color tint evident in the earliest pornographic films. Those films were in black and white, and the bluish tint appears when quick and cheap ways were used to develop the film.
• As  someone mentioned that the following theory may also be true:         The term "blue film" or "blue movie" refers to a cinematic production that is contrary to the standard moral code. It is probably a spin-off from the "blue laws" that existed in many states until about 50 or 60 years ago. In the late eighteenth century, Rev. Samuel Peters introduced the term as a reference to the "bluenoses" who subscribed to the Puritan standards of the seventeenth century. Rumors claim that he wrote on blue paper or that his writings were found in books with blue covers. Neither rumor has been substantiated.According to the "blue laws," most businesses could not operate on Sunday. "Keeping the Sabbath holy" was one of the ten commandments, the basis of most laws in Christian countries.The blue laws particularly targeted the sale of alcohol, but they also applied to grocery stores and other commercial activities.However, pharmacies were exempt in most cases because of the emergency need for medication. That's why, today, many items that would be sold in super markets or dry goods stores are found on the shelves of Rite-Aid, Long's, Walgreens, etc As times and community standards changed, so did the laws. Consequently, most people today have never heard the expression "blue laws" and would not have any idea of why XXX films would be called "blue movies."- All this one na story✌✌✌

Culled from Quora!