Chroma key algorithm with unknown background color

1. What are the two most common colors used for chroma keying?
2. Can chroma key be colored?

What are the two most common colors used for chroma keying?

Green and blue tend to be the most common colors used for chroma keying because they're opposite of our natural skin tones and hair color. Of the two colors, green tends to be preferred over blue because today's video cameras are most sensitive to green, giving the cleanest key effect.

Can chroma key be colored?

Although green and blue are the most common in part because red, green and blue components are used to encode the visible light spectrum, any key colour can be used.