Some of us saw it in school, some in college, while the rest of us took a little longer. But it is safe to say that we've all seen porn, at least once.
Given how big a deal sex is in our country, porn obviously has a discreet undertone to it as well. It is not openly accepted in our society and so the subtler term that we have been using for it is 'blue film'. But why only blue film?
Well, Quora has some answers.
Earlier, when there were B-grade or porn movies playing at local theatres, posters were printed in blue & white to not attract attention like normal movie posters do. In fact, this is still practiced at some places.
Another story says that when porn movie shoots were initiated, they weren't easy to make. Budget was an issue. So movie makers and producers had to resort to cheaper ways to develop the black & white reel into a coloured one. And it is because of this that they had to compromise the quality of the film and give it a blueish tint, instead of a proper colour.
It was also likely that producers bought damaged movie reels at cheap prices, which would also result in a similar blue tint indicating the low quality. Although, now you can watch it in HD, the name 'blue film' stuck.
There could be one more reason - one that is quite popular for the origin of the term. It's based on how video stores used to differentiate between normal movies and erotic/adult movies. The stores would actually sell VCR cassettes in blue packs as opposed to paper bags or normal polythene packets, thus denoting these videos with the colour blue.