Trichromatic theory suggests that:

Trichromatic theory posits that color vision is facilitated by three types of photoreceptor cells in the retina, each sensitive to different wavelengths of light corresponding to red, green, and blue-violet. This theory was developed based on the observation that all colors perceived by the human eye can be created by mixing these three primary colors of light. When light hits the photoreceptors, varying degrees of activation among the three types lead to the perception of different colors, reflecting how our visual system processes color information.

The identification of these three distinct types of receptors as specifically responsive to the three primary colors provides a foundational understanding of how humans interpret the color spectrum. This theory helps explain a wide range of color vision phenomena but is complemented by other theories, such as the opponent-process theory, which addresses how colors are perceived in relation to one another in the brain.