how does a green screen work? Why is it green? Answered

It does not have to be green. The technique can be done using any color, even colors which are outside of the spectrum of human vision (as long as you develop a camera that can pick it up). Green is used often because it's easiest for most modern cameras to pick up, giving the editor the cleanest possible image. It's also a less common clothing color, meaning it's less likely to cause any embarrassing disappearing outfits. Blue was once common, but it's common in wardrobes and is a common eye color. Still, you can avoid this, and it's a good color to try because it shouldn't interfere with skin color. White is a bad color because it's common in wardrobes and eyes. Same for black, only add to that hair. Both of these play a strong role in lighting and shadowing. Avoid these. Red is a bad color because it's seen in your lips and mouth and your skin tone. To select a good color, pick one that's not going to be found on anything else in the scene. Almost neon colors work well because they're bright and strong. For materials, anything matte and flat is good. Shine, reflections, and heavy texture is bad. How does it work? With digital processing, it gives the editor a solid background that's easily removed by software. Speaking of which, most consumer video software with chromakey capability (Adobe Premiere for example) will allow you an option to select any color to be removed.

The green screen should be a more technical matter rather than some long
dissertation of what it does in Hollywood. A dedicated camera is aimed at a  green colored background and sends this information to a switcher or a chroma key device.  The switcher  receives the chroma  information from the dedicated camera that is producing a very high voltage output from the green  screen. This information "green" is now going to be compared to the switchers green color, and when both the switcher's color green and the camera's color of green are the same, but 180 degrees out of phase, the camera's color "green" is dissolved and is eliminated. Why did the green
color of the camera disappear?  When two voltages meet and are 180 degrees out of phase, the camera's green was eliminated allowing for
a matte or some other video to be super imposed as a back ground. If a
subject was in the dedicated camera's shot, all but the subject would remain. Just electronically removed to allow an overlay to be added later.
I hope this is helpful in telling why it works.

It's green I believe as bright green isn't really a common colour to wear.

If you want to try some chromakey use debugmode wax, It's free and you can change the colour of the key to whatever you want. Some great fun to be had if your bored

Look up "chromakey" on Wikipedia.