What theory suggests that the retina contains three different color receptors, sensitive to red, green, and blue?

The theory that suggests the retina contains three different color receptors sensitive to red, green, and blue is known as the trichromatic theory. This theory was first proposed by Thomas Young and later expanded by Hermann von Helmholtz. According to this theory, the perception of color is achieved through the activation of these three types of cones in the retina, each of which is tuned to respond best to one of the primary colors: red, green, or blue. When light hits the retina, the different cones respond variably depending on the wavelengths of light, and the brain interprets the combined signals from these cones to create the full spectrum of colors we perceive.

The trichromatic theory effectively accounts for how we can perceive various shades and colors from just three types of receptors, playing a fundamental role in our understanding of human color vision.