Wednesday, April 27, 2016

Weirdness of The Colour Spectrum

Visible light, on passing through a prism, gets separated into its component colours of a rainbow pattern. That pattern is called the Spectrum of Visible Light; it includes Red, Orange, Yellow, Green, Blue, Indigo and Violet. Each colour in this spectrum has a unique wavelength and that is its identity. 

Magenta, on the other hand, is an improbable colour! The weird thing about Magenta is that we do not see it in a the spectrum of visible light, which should technically include all the colours that are in the visible light wavelengths.

We see images due to the reflection of the image in our eyes. As the reflected light enters our eyes the Retina stimulate the brain. To see colours the reflected light stimulate a special kind of cells called cone cells. The cone cells send the signal to the brain and we get to see what colours we see. We humans possess three type of cone cells dedicated to Red, Green and Blue light. When we see an object that is Blue in colour the Blue cone cells are activated and they send a signal to the brain, likewise, when we see Red or Green objects the brain receives stimulus from the respective cone cells. 

Those are the three Primary colours that we see and every other colour is a combination of those colours. So when we see a yellow object Red and Green cone cells are activated and our brain perceives it to be something in between Red and Green on the visible light spectrum. Similarly, when we see Cyan the Blue and Green cone cells are activated simultaneously, as cyan is in between Blue and Green (the primary colours that we are capable of seeing)  

Our eyes cannot measure the wavelength of light directly. So we have three check-post on the spectrum namely Red, Green and Blue. Depending on the stimulated cone cell type we see the picture of objects as our brain perceives it. 

Now let us assume we see an object and our is stimulated by both Red and Blue cone cells. The colour we should be seeing must be something in between the Red and Blue on the above spectrum. However, the colour in between the Red and Blue is Green! But there is no Green colour clearly, as it would have stimulated Green cone cells. In such case, the Brain makes up a colour! That made up colour is (drum rolls please) Magenta! 

On the level of wavelengths, magenta does not exist! it is just the same old white light with the absence of green wavelength! Every other colour we see has a dedicated wavelength but magenta is a construct of the human brain and is purely perceptional. 

So how do we know that we all see the same colour as "Magenta"! or any other colour, for that matter! We all grew up being taught that the Sky is Blue and the Grass is Green. We learned our colours in a way that is highly subjective. We were taught on the basis of what we see. So, how can I be assured that my Blue and your Blue looks the same? Well, the answer to that is: We cannot be assured that we see colours in the same way! Colours are mental perceptions and there is no way (yet) to find out that we indeed see same colours. 

Some experts argue that the inability to explain colours in words is the problem and suggest that it is a lingual failure. Frankly I don't know if that is more comforting or seeing colours personally is more pleasant of a thought! All our perceptions, be it colours, taste or olfactory sense are our own we do not have any way to testify if we all sense and perceive things in the same way. In a way, we are all alone in out brains. However, we find ways to relate and connect and that is the beauty of it, we are all in this together. 

To solve the confusion on magenta not being in the visible spectrum we often use a conceptual representation called the colour wheel. It is bending the visible spectrum in a way that makes Red and Violet meet. Another  cool conceptual representation is this book called the colour atlas. Is it just me or do you also see a little hint on unperceivable higher dimensions? Alright, just me then!


PS: If your favourite colour is magenta, get over it! Technically it is not even a real colour.  

Colour Mixing 

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  1. Wow, this was pretty amazing! Maybe this explains why I can never mix this shade with my paints! I am so going to flaunt this new-found knowledge, majenta ain't no color people!
    @KalaRavi16 from

  2. Dang it! My magenta is not even a real shade.