These three colours, red, green, and blue, are called the primary colours for human colour vision. When we look at a ray of light that excites only the red cone, we see red. The light that excites only the green cone appears green; and the light that stimulates only the blue cone appears blue.


All the other colours that we see result from the stimulation of the combinations of these three cones. For example:


  • Light that excites the blue and red cones equally results in magenta, which is a deep pink colour.
  • Light that excites the blue and green cones equally results in cyan. Cyan is a blue-green colour.
  • Light that excites all three cones equally appears white.


Thousands of colours that we see result from the stimulation of these cones in different combinations.


When we see something, an image enters the eye in the form of light and is projected onto the surface of the retina. The light signals travel through the cells on the surface of the retina and flow down into the rods and cones. The cones can distinguish colour from the frequency of the light being reflected off of the viewed object. The rods and cones convert the light wavelengths into nerve impulses or nerve signals. The photoreceptors then send these nerve signals to the optic nerve, which carries them to the brain. The brain then translates these signals into what we perceive as sight.



O'Haver, Tom. ”In Living Color: The Science and Mathematics of Color.” Inform@Maryland. Jan. 2001. Web. 17 Feb 2013. <>.


"Human Body Facts." Science Kids. 25 Feb., 2013. Web. 19 Apr. 2013. <


How do humans perceive colours?


The retina in the human eye contains two types of vision cells or photoreceptors: rods and cones. Rods are long, cylindrical cells that allow us to see at night, and they also detect shapes and forms. The cones, on the other hand, are for colour vision and allow us to see during day time.  


There are three types of cones:


  1. Red  cones are sensitive to red light.
  2. Green  cones are sensitive to green light, and
  3. Blue  cones are sensitive to blue light.