The Tri-chromatic theory is based on the assumption that the three classes of cone receptors sub serve the colour vision. This theory dates back to 18th century and was popular during the first half of 20th century and was often used against the opponent processes theory. It was also known as Young-Helmholtz theory of colour vision, according to this theory there are three receptors in the retina that are responsible for the perception of colour. These receptors have different sensitivity level. Blues ones are the most sensitive and the red ones the least. But to perceive the colour needs the interaction between at least two photo receptors. Then the three colours are combined to form any colour in the visible spectrum.
