You might have seen in the behind the scenes pictures of numerous films and shows that the unrealistic scenes or dummy are shot with green coloured backgrounds. Have you ever wondered why the background is green and not any other colour such as red, pink, purple or white?
Green is the go-to colour because it is indifferent to nature. It doesn’t match any hair colour, natural skin colour or body part making it easier to edit. In this way, no part of the human body is edited out in the chroma key. However, if a green costume or prop is required the green screen is replaced with a blue screen.
The colour green is pretty odd and stands out. So if the actor is wearing a pink dress in front of a pink background then the chroma key while replacing the background with an image would pick the dress’ colour to replace as well. Green screens are also more commonly used because of the colour green being the highest luminance among all the colour channels (RGB).
Nowadays blue screen is used in place of green screens because blue is a much softer colour. They are easier for chroma-key too.
The shooting of blue screens and green screens differ on the basis of what is in front of the screen. You cannot shoot a green parrot in front of the green screen and similarly, you cannot shoot the blue avatar characters in front of blue screens. Like when they shot Green Lantern or Hulk they definitely used blue screens. It is always good to have options in handy. Use of chroma key is taught to you in visual effects courses.
In post-production studio, VFX artists use chroma-key to edit the screens and replace them with required background and images. The dragons on Game of Thrones are nothing but props with green coloured wraps. They later appear on the screen as dragons carrying the Queen of seven kingdoms.
Now that you know the real reason behind adding the green/blue screens for special effects it is no more confusing why other coloured backdrops are not added.