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Magenta Ain't A Colour

Magenta Ain't A Colour

By Liz Elliott

A beam of white light is made up of all the colours in the spectrum. The range extends from red through to violet, with orange, yellow, green and blue in between. But there is one colour that is notable by its absence (click here to check). Pink (or magenta, to use its official name) simply isn’t there. But if pink isn’t in the light spectrum, how come we can see it?

Here’s an experiment you can try: stare at the pink circle below for about one minute, then look over at the blank white space next to the image. What do you see? You should see an afterimage. What colour is it?

You should have seen a green afterimage, but why is this significant?

The afterimage always shows the colour that is complementary to the colour of the image. Complementary colours are those that are exact opposites in the way the eye perceives them.

It is a common misconception that red is complementary to green. However, if you try the same experiment as above with a red image, you will see a turquoise afterimage, since red is actually complementary to turquoise. Similarly, orange is complementary to blue, and yellow to violet.

All the colours in the light spectrum have complements that exist within the spectrum – except green. There seems to be some kind of imbalance. What is going on? Is green somehow being discriminated against?

The light spectrum consists of a range of wavelengths of electromagnetic radiation (check this too). Red light has the longest wavelength; violet the shortest. The colours in between have wavelengths between those of red and violet light.

When our eyes see colours, they are actually detecting the different wavelengths of the light hitting the retina. Colours are distinguished by their wavelengths, and the brain processes this information and produces a visual display that we experience as colour.

This means that colours only really exist within the brain – light is indeed travelling from objects to our eyes, and each object may well be transmitting/reflecting a different set of wavelengths of light; but what essentially defines a ‘colour’ as opposed to a ‘wavelength’ is created within the brain.

If the eye receives light of more than one wavelength, the colour generated in the brain is formed from the sum of the input responses on the retina. For example, if red light and green light enter the eye at the same time, the resulting colour produced in the brain is yellow, the colour halfway between red and green in the spectrum.

So what does the brain do when our eyes detect wavelengths from both ends of the light spectrum at once (i.e. red and violet light)? Generally speaking, it has two options for interpreting the input data:

a) Sum the input responses to produce a colour halfway between red and violet in the spectrum (which would in this case produce green – not a very representative colour of a red and violet mix)
b) Invent a new colour halfway between red and violet

Magenta is the evidence that the brain takes option b – it has apparently constructed a colour to bridge the gap between red and violet, because such a colour does not exist in the light spectrum. Magenta has no wavelength attributed to it, unlike all the other spectrum colours.

The light spectrum has a colour missing because it does not feel the need to ‘close the loop’ in the way that our brains do. We need colour to make sense of the world, but equally we need to make sense of colour; even if that means taking opposite ends of the spectrum and bringing them together.

Well, now we've got that sorted out, explain this: stare at the dot in the middle of the image below - you should see all the colours melt away. 

Bye for now - why not join our Facebook group?  Alternatively find more Unlikely Science here.  You can find out more about Liz on her Nullpage.

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Your Say

Turquoise? I'm sure you meant cyan, that's the CIELAB official designation.

Your headline is not exactly correct - it should read :Magenta ain't got a wavelength.

You can do this in photoshop, just do RGB layers and then use the opacity feature to fade. Red + Blue = Magenta. Green + Magenta = Grey, which is the expected result because a 50% mix of each RGB is grey and white is a 100% mix and black is a 0% mix.

As the article says, colour is just a creation of our minds from its interpretation of the wavelengths of visible light. The green wavelength of light is most visible because it stimulates first the M (green) receptors in the eye, then the S (blue) and L (red) receptors equally. However magenta/pink stimulates first the S and L respectively, and then the M receptor. So the brain interprets the two signals differently, as it should, and we interpet these kinds of colours as hues.
Electromagnet via Reddit

I stared at that dot for four minutes and the colors stayed right where they were.
Autoclave via Reddit

What happens to color-blind people when their mind tries to fill the gap between the colors they do see?

Guess what? I took a black & white print-out of this image and focused on the dot, everything vanished again!... Now, this probably means that its got nothing to do about the colors, but this image is probably just a stereographic image!

If you knew what a stereographic image is, you would know whether or not this image fits the definition. It does not. Don't go flinging words about that you don't understand my boy.

Could all this explain why my bedroom appears bright green some sunny mornings when I first open my eyes?

The vanishing color actes very simply. You know when you stare at a light bulb, and you look away, you see a spot that is really annoying 'cause it blocks what you can see? Also recall the green after image of magenta. When your eyes see a color for a long period, it will trick your brain into thinking that it is not supposed to be there, it tells it to show an equally opposite color of that, overlaying the color thats there. That makes a gray, white or black depending on the brightness. So if you stare at anything, it will eventually disappear if against a solid background(also why some old people loose eyesight :P)

Your headline and description fail to fairly describe the article. However, the fact that Magenta is a purely subjective colour is really something. If any of you read Valis by Philip K. Dick you'll remember that it is the color of the "god", and the color is also a recurring theme in other works (Transmigration of Timothy Archer). It's not the exact christian god, but PKD's conception of the one who makes the grass green. Think about it. This color isn't there, and it doesn't correspond to a "mathematical" approach to perception, which would be to see things as green. It's 100% made up inside our minds!
Plugues on

Ok, I stared at the dot and yes I saw green when I looked at the white part. I went into trusty photoshop and made a green color. I did the same thing. I saw magenta when I looked away.

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31 Jul 2011
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