The eye is made up of various receptors to perceive colour called rods & cones. There are over 120 million rods and 7 million cones in each eye.
Rods are more sensitive than the cones but they are not sensitive to colour, they perceive images as black, white and different shades of grey.
Cones contain one of three pigments sensitive to either RED GREEN or BLUE.
When light is reflected off a subject into your eye, the wavelengths of reflected light hit the light sensitive retina in your eye which is covered by these millions of light-sensitive cells (rods & cones) and stimulate these cells to varying degrees which sends a signal through your optic nerve into the cortex of your brain which work in combination with connecting nerve cells and give the brain enough information to interpret and name colors and familiar sensations of color to determines the colour of the subject.
64% of cones are Red Receptors which are sensitive to long wavelengths (red). One third of cones are Green Receptors which are are sensitive to middle wavelengths (green) and 2% of cones are Blue Receptors which are sensitive to short wavelengths (blue)
When each of these cones are stimulated at varying degrees they differentiate the colours as per below.
Red & Blue cones stimulated produces magenta light, (magenta is a secondary additive colour)
Red & Green cones stimulated produces yellow light, (yellow is a secondary additive colour)
Blue & Green cones stimulated produces cyan light, (cyan is a secondary additive colour)
Red, Green & Blue cones stimulated produces white light.