hi david,
at the site it said,
"Take a moment at this point to also ensure that you have completely eradicated from your mind every trace of the primary school notion that green is "made of" yellow and blue. Subtractive mixing doesn't work like that. We get a green mixture from yellow and cyan because our components are both in part "made of" green. If any colour can be said to be "made of" yellow and blue, it's white."

"If any colour can be said to be "made of" yellow and blue, it's white" did you mean it black? cause yellow and blue has not wavelength in common.
thanks before david.