Are you talking about green screens?

Mostly because computers can easily distinguish green from human skin and hair colors. That makes it easier to make the green parts of a video transparent without accidentally removing human parts..

I guess, it isn’t always a screen, sometimes people wear suits and what not

You can't use red because it is too close to human skin.

So that leaves green and blue. Both have been used in the past, but people wear blue or bluish clothes more often than green. Same for props and furniture.

Plus there's some preference for green due to certain compression methods.

Wiki article for details

Because the eye is most sensitive to green. So in order to save processing video is encoded as a "base" green as luminance. The eye is most sensitive to luminance (how dark/light something is). The other colors, blue and red are then encoded using less data per color. This creates what is called YUV or YCrCb encoding. In short, it is a form of data compression capitalizing on our green sensitivity. see https://en.wikipedia.org/wiki/YUV

The idea is to have a color which is unique to the background or a portion of the image which is to be removed or altered. Blue is another color commonly used but red is avoided because humans tend to be somewhat pink in our fleshy bits which could be confused for the screen.

Another benefit of using green is that many digital image sensors have more green subpixels than blue or red. This is because the human eye is most able to detect differences in shades of green so maximizing fidelity in that range yields a better image. But this also means that cameras effectively have a higher resolution for the color green so a mask made using that color can be better than with a different color.

If you need to erase a bunch of the image, to replace it with something else, it's easier to do if the parts you want to get rid of are a bright, distinct color.

So if you're making a Marvel movie and your actor is supposed to be on an alien planet, but you're going to add the planet later, you film the actor in front of a bright green background. Then you can take out all the green and you have your actor on their own and you can drop them into the alien planet that you created in the computer afterwards.

Green is the most common color because it is far away from human skin, and not a color we normally wear. You will sometimes see blue, or even purple used instead depending on what is being filmed.

I don’t know if it’s still the case, but when I used to read up on video cameras, the sensors used a Bayer pattern that had twice the resolution for the green channel as the red and blue channels. This leads to the green channel having more detail for chromakeying.

“Invented by Bryce Bayer at Kodak, the Bayer pattern dedicates more pixels to green than to red and blue, because the human eye is more sensitive to green. The additional green pixels produce a better color image.”

Bayer Pattern Sensors

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It's the most common because you're usually shooting humans who are more reddish, and green is on the opposite side of the color wheel from red.

But blue screens and red screens exist for the technique of chroma-keying for niche situations (ex: needing to chroma key something that is heavy in blue and green, bust out the red screen). It's just that green plays the nicest with the most commonly filmed things.

The purpose of green screens is to give a solid background that is easy to remove in video editing software. Green is an idea color for this purpose because it's a primary color for human vision that does not show up in any appreciable amount in human skin tones. Human skin tones are mostly red, so blue is also viable, but green ends up working better because reddish-green or greenish-red isn't a thing for human vision.

With modern video editing, you could use any color. That bright green color is used because it's quite a bit different from tones in skin and natural tones, and it's easy for equipment to identify the color and get a good separation between the background and the subject.

With older equipment, green had the added benefit of being the "base" color for the video signal (and other colors were created by adjusting red and blue levels). This meant the equipment was particularly sensitive to this color and it was easier to make equipment to lock in on it and treat it as transparent.

Up through the 1980's the same effect was done with film and using the color blue and special filters to make "film sandwiches" that could combine multiple images into one picture. The technique had been used since the 1930's, but it became more sophisticated with each decade.

This is all correct, and as a bonus fun fact, the reason blue screens were previously more common is because film is less grainy on the blue channel. So the shift from blue to green coincided with the shift to digital.

One of my favorite Captain Disillusion videos explains the history of green screening and why we use that vs, I dunno, red https://youtu.be/aO3JgPUJ6iQ

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Process of elimination:

Black - all shadows and anyone with dark hair is not transparent.

White - really pale people, your eyes, apper are all now transparent.

Red - If you blush or are a bit sunburned, you're now semi-transparent.

Yellow/Orange/Purple - all have a ton of different shades so are harder to key on (with older set ups).

Blue and Green are pretty commonly used. Blues though are pretty common in both genders for clothing - though some news sets will have more than one screen to allow the presenter a choice in clothing.

Green also gets bonus points for reflecting light really well from artificial light sources.

Now - you might point out that we have really powerful computers and lights you can set to any frequency you want now. So - honestly - we could use ANY background we want as a "green screen". And, we totally can. Heck, programs like Zoom can identify things in the background and just get rid of them without even taking color into account. However, we continue to use green because it's just what we've always used and technicians, wardrobe and presenters are used to the quirks, so it's more common.

Another bonus fact, the reason the human eye is more sensitive to green is because we evolved in trees as primates. Science yo.

Green is on the opposite side of the color wheel from skin tone, so it is the easiest to “key out”.