system
Given the following post, respond as if you're commenting on Reddit:
human
ELi5:why are greens screens always green or blue? Are other bright colours also usable for the same purpose. If not, why not.

Whenever they show behind the scenes clips of movies the parts where CG is added are always coloured a bright florescent green and less often a sky blue colour. Why are these colours significant and are there other options that are more seldom used?
gpt
Because blue and green are the least likely to show up in skintones. In the old days ( black and white movies ) they also used red screens. But since red ( and any other color but blue and green ) are commonly found as a shade ( for exaple skintones ) filmmakers opt for blue or green.