Opponent Theory of Color Vision

In 1870, Ewald Hering, a German psychologist / physiologist proposed an alternative theory of color vision. Based on a series of subjective observations of color appearance, Hering proposed that color vision was derived from three mechanisms; one responding positively to red light and negatively to green, one responding positively to yellow and negatively to blue and a brightness mechanism which responds positively to light and negatively to the absence of light. This theory became known as Hering's theory or the opponent theory of color vision.