You don’t require green for a green screen.
The main necessity for a “green screen” is to have a variety unmistakable enough from everything else in the frame
The reason for that is that after shooting a video, while editing, you want your video editing software to easily understand what it should keep(like characters in the foreground) and what it should replace with a pre-made background. The easiest way to do this is to tell it “replace everything of this color and keep everything else”.
You can see in the screenshot above the editor’s mouse over the left picture. They are choosing the color (blue in this case) that should be replaced. The result can be seen in the right image.
This process is called chromakeying.
In fact, the color itself is not even the only option to do keying. You can use any other property of a picture, like brightness, saturation, etc. You can even combine them in the complicated scenarios, for example you can tell the software to “replace everything of dark saturated green with this image and everything light low-saturation in the range from yellow to red with this image”.
The reason why green is so popular for this use is that it is pretty much “the opposite” color to the spectrum of human skin shades, and the more contrast you have between what should be kept and what should be replaced in the picture, the better chromakeying will work.
