As she continues, you realize she is explaining the "trichromatic" theory of color vision.
There are two main theories that clarify and guide study on color vision: the trichromatic and the opponent-process theory. These two theories are integral and clarify forms that work at various levels of the visual framework. As per the trichromatic theory of color vision there are three receptors in the retina that are in charge of the impression of color. One receptor is touchy to the green, another to the blue and a third to the red.