If I can paint ANY color on a background to use for a chromakey, how do I determine the best color? I know people use green and blue and sometimes red, but what if there is a color that is even more distinct from my subject than those colors?
Can it be determined by shooting an image then inverting it to see the "opposite" color? Or is the reason green, blue, or red are commonly used because of the RGB color space?
I am asking because I am shooting stop motion of a toy fish which has some greens and browns in it. So I'm not concerned about skin tones at all. And I need to paint a background and I figured I could do blue, but maybe there's an even better color?
Digital cameras have their sensors arranged in a pattern known as the Bayer Filter, this provides twice as many green sensors as blur and red ones. So if you’re trying to get the most information into your keying software, shooting with green screen will get you the best result.
RGB because those are the sensors in the camera. Every other colour is a mix of one of those.
Film was found to be able to be most responsive to blue when developing, so blue screens could be turned black while other colours could be made white. This allowed film makers to generate mattes they could then use to cut out the blue backgrounds.
Captain Disillusion does a brilliant, humorous video explaining at lot of this stuff:
To answer your question though - you can indeed use any colour for your keying. Strong, even lighting is often more important. Strong/bright gets more information into the camera, Even to prevent different shades.
If you’re shooting on a smart phone or tablet, check out the Mavis camera app as it includes a Vector Graph so you adjust your camera before shooting.