I recently heard the following presentation on the BBC about one of my favorite colors – and I found the explanation of this brilliant hue to be quite enlightening and interesting. In order to share it with all of you, I’ve written it down here; the words are mostly those of the BBC, with a few of my own. I hope you enjoy it!
~ Lee 

If you look at a rainbow what color is noticeably missing? It’s magenta…. it’s not there. How then do we see it? 

Our brains are information processors. The brain converts the billions of events going on around us. It then interprets all of the info going on in the world around us into signals, which we can make sense of through our senses. The brain allows us to interpret these signals into sounds, smells, and so on. One of the things going on around us is what is referred to as the electromagnetic field. There are waves of energy that ripple across this field. The frequency of these fields determines a range of effects. These consist of radio waves, infrared waves, UV waves, Xrays, and Gamma rays.

For example, these magnetic fields help to heat our food in the microwave and listen to voices and other sounds broadcast through the radio. We are, however, only able to detect a tiny portion of the wavelengths. 


We mostly detect these particular waves through our eyes (and some through skin via a sunburn). The wavelengths we see are called “visible light”. The visible light spectrum in humans is 700 nanometers to 400 nanometers. We aren’t even certain as to why this is but we can hypothesize that the reason we see these is because they are the waves that can easily travel through water. It is also the part of the EM spectrum that the sun emits the most of. Given that our earliest ancestors lived in the sea and were illuminated by the sun, it makes the most sense that we would evolve to detect the most common and useful of these wavelengths in the EM spectrum.

From Waves to Color

Our eyes detect color via specialized cone cells. There are typically three types of cone cells in humans. Cones that detect short wavelengths (blue), medium (green), and long (red). However, we do see more than just the red, green, and blue colors. The cone cells in our eyes overlap in the wavelengths they detect.  

From BBC

Look at this chart; you can see that when a wavelength of 570 nanometers enters the eye, it stimulates both the long and medium cones. The responses are combined and sent along the optic nerve as one signal. And it is this signal that we interpret as yellow light. An odd quirk of this system is that when two beams of light at the exact same ratio enter the eye the signal that is sent off to the brain is the same. These two combined light rays also cause us to see yellow.

A computer screen takes advantage of the way our brain perceives color. Screens are composed of small clusters of red/green/blue lights, yet the screen display can produce the entire color spectrum. Every color that we perceive can be generated by this dual route. A single wavelength of light or a combination of wavelengths of light stimulates our cones in the same manner… except for one.

The Odd One Out

Magenta… there is no wavelength of light for magenta. Instead, we perceive it only when the short and long cones pick up a signal from pure red and pure blue light. Our brains literally make up magenta. Why?  We don’t know. It is probably quite useful, however. Much of our early primate ancestors inhabited green forests. Magenta flowers would have had the highest contrast against a green background making it easy for our ancestors to find a tasty snack.

Our brains regularly take all kinds of cognitive leaps all the time. You may be surprised to learn that all around you in the world isn’t exactly as it appears. Magenta happens to be one of these anomalies.

To watch the original video, click here

Video by Archie Crofton

Narrated by Lotte Rice

Commissioned by Paul Ivan Harris