Six Colour Rainbow?

[GNC]

I've dredged this factoid up from somewhere today, but the story goes there are not seven colours in the rainbow, there are six. Indigo and violet are shades of the same colour you see, and the only reason people said there were seven was because that was a "holier" number than six. Sir Isaac Newton's religious bent was supposedly behind this.

Was there any truth to it? I must admit I have trouble seeing much difference between indigo and violet in a rainbow.

 

[EnolaGaia]

I've always heard / read that Newton's choice of 7 colors for his color diagram in _Opticks_ derived from a desire to correspond to the number of notes in a musical scale.

My understanding was that indigo was widely removed as an essential color category because the human eye is relatively poor at distinguishing hues in that middle ground between blue and violet, and in practice few people could distinguish indigo as a separate color / category.

 

[Recycled1]

The colour orange results from blending red and yellow, and the colour green results from blending yellow and blue. If you blend red and blue you end up with what is usually called "purple". Surely that's what the indigo /vilolet combo should simply be called?
I've sometimes wondered why "turquoise", the combination oif green and blue, was missed out!

I've got a set of those little '50's "tot" glasses in rainbow colours - there's only six of them(r,o,y,g,b,p.)

 

[Pietro_Mercurios]

Goethe did a whole treatise on the nature of colour perception, after Newton. On the one hand, Newton tried to fit the observed spectrum into theories of mathematics and science, on the other, Goethe, a poet, was interested in the nature of the human perception of colour, as the interplay between the polarities of light and darkness on the human eye.

http://en.wikipedia.org/wiki/Theory_of_Colours

... For Goethe, "the highest is to understand that all fact is really theory. The blue of the sky reveals to us the basic law of color. Search nothing beyond the phenomena, they themselves are the theory."[17]

...

Who does he sound like? :lol:

Like Fort, Goethe was an arch-phenomenologist.

http://en.wikipedia.org/wiki/Theory_of_Colours#Current_status

Current status

Goethe started out by accepting Newton's physical theory. He soon abandoned it... finding modification to be more in keeping with his own insights. One beneficial consequence of this was that he developed an awareness of the importance of the physiological aspect of colour perception, and was therefore able to demonstrate that Newton's theory of light and colours is too simplistic; that there is more to colour than variable refrangibility.
—Michael Duck, 1988[38]

As a catalogue of observations, Goethe's experiments are useful for understanding the complexities of human colour perception. Whereas Newton sought to develop a mathematical model for the behaviour of light, Goethe focused on exploring how colour is perceived in a wide array of conditions. Developments in understanding how the brain interprets colours, such as colour constancy and Edwin H. Land's retinex theory bear striking similarities to Goethe's theory (Ribe & Steinle, 2002).

A modern treatment of the book is given by Dennis L. Sepper in the book, Goethe contra Newton: Polemics and the Project for a New Science of Color (Cambridge University Press, 2003).[30]

...

Although Goethe's ideas and observations about the perception of colour don't really amount to a scientifically rigorous theory, they have stood the test the test of time remarkably well. They've also been influential in all sort of areas of art, aesthetics, psychology and philosophy.

He also realised how important the non-Newtonian spectral colour, magenta, was for the human perception of colour. He worked out a whole system of complimentary colours in his colour wheel system. Proving that, 'One measures a circle, beginning anywhere'.

http://en.wikipedia.org/wiki/Theory_of_Colours#Goethe.27s_colour_wheel

Goethe expressed his understanding of the light and dark spectra in including magenta in his colour wheel. Whereas for Newton magenta was an 'extraspectral' colour, for Goethe magenta was a natural result of violet and red being mixed in a dark spectrum (top of wheel), just as green resulted from the mixing of blue and yellow in the light spectrum (bottom of wheel).[24]

"For Newton, only spectral colors could count as fundamental. By contrast, Goethe's more empirical approach led him to recognize the essential role of (nonspectral) magenta in a complete color circle, a role that it still has in all modern color systems."[25]

...

Where would colour TV, or inkjet printers, be, without magenta?

Well worth checking out the Wikipedia entry on the subject.

http://en.wikipedia.org/wiki/Theory_of_Colours#Current_status

If there are any influential thinkers worth being studied by serious Forteans, Goethe is definitely one of the front runners.

 

[GNC]

Maybe I should have posted this in the Science forum! Pink isn't in the rainbow, though I suppose it's a kind of magenta. Brown isn't either, so I suppose if we relied on the rainbow there would be great amounts of people we wouldn't be able to see at all.

 

[PeniG]

Maybe I should have posted this in the Science forum! Pink isn't in the rainbow, though I suppose it's a kind of magenta. Brown isn't either, so I suppose if we relied on the rainbow there would be great amounts of people we wouldn't be able to see at all.

Now that's an interesting explanation for the racism by omission of the media!

 

[escargot]

I've read somewhere that perceptions of colours in rainbows are culturally defined, so that varying colours and numbers of colours are seen by different ethnic and language groups.

Welsh people, I seem to remember, have a different experience of rainbows from an English person's because they see and name other colours.

 

[Recycled1]

I've been trying to remember how to "make" brown from powder paint in the infant classroom. I think it's a combination of red and green, which would explain why we don't see it occuring in the rainbow.

 

[GNC]

That's right, brown is a mixture of all the artist's primary colours, so red, blue and yellow together, or red and green which is the same thing. The primary colours of physics are red, blue and green though, dunno if it's the same combination for brown there.

 

[Xanatic_]

Remember that wavelengths and colours are not the same thing. I believe some things have the same wavelengths but are percieved as different colours. Brown and orange apparently.

 

[OneWingedBird]

The primary colours of physics are red, blue and green though, dunno if it's the same combination for brown there.

All three primary colours in equal amounts makes white, in physics.

I will confess to one day thinking that might work in the paintbox as well and trying it out, end result looks like crap.

 

[rynner2]

rynner throws hands in the air in despair at the confused and un-scientific understanding revealed in this thread!

There's a spectrum of colours in the rainbow which derive (simply) from the frequency of the light involved. How people name these colours (and exactly how many they distinguish) is up to them, but frequency/wavelength is the defining characteristic of each 'colour' in the spectrum.

But bringing in discussions of 'pink' (ie, pale red), or 'brown' (a mixture of colours) just confuses the issue, as these don't appear in a rainbow. We can however simulate these colours in a computer by R/G/B combinations:
http://en.wikipedia.org/wiki/RGB_color_model

Website producers may well be familiar with the hexadecimal numbers representing different colours.
http://en.wikipedia.org/wiki/RGB_color_ ... sentations

So not all colours appear in the rainbow, but all colours can be represented, to whatever degree is required, by various computer specifications.

 

[Pietro_Mercurios]

Yep! The visible light spectrum is only a small part of the electromagnetic spectrum of radiation. It ranges from sub-radio waves at one end, through microwaves, to near-infrared, visible light, ultraviolet, X-rays, through gamma rays.

https://en.wikipedia.org/wiki/Electro-magnetic_spectrum

The reason we see visible light the way we do, is partially because of the way the sun emits visible light with a signature spectrum, of varying wavelengths, mostly a byproduct of the fusion of hydrogen atoms into helium and the way the physiology of the human eye has evolved, with its system of rods and cones, sensitive to light and dark and colours, within what we know as the visible spectrum. Rods are sensitive to light and dark, but not colour. Cones are sensitive to colour and there appear to be three different kinds of them in most human eyes. People with only two different types of cones appear to suffer from colour blindness.

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html

People have been identified with four different kinds of cones, so called tetrachromats, they may see a somewhat different, more complex, colour spectrum.

https://en.wikipedia.org/wiki/Tetrachromacy

Various animals are also tetrachromats and can see different parts of the electromagnetic spectrum. Bees, for instance, appear to be able to see into the ultraviolet.

The reason colour pigments in paint don't mix true to pure visible light spectrum colours, is because the pigments used in paints are not really pure colours, but mixtures of various kinds. They don't emit light, but reflect it, or absorb it, in certain wavelengths.

 

[Recycled1]

Rynner are you going to tell me that there's no pot of gold at the end, either?

 

[Zilch5]

Yep! The visible light spectrum is only a small part of the electromagnetic spectrum of radiation. It ranges from sub-radio waves at one end, through microwaves, to near-infrared, visible light, ultraviolet, X-rays, through gamma rays.

https://en.wikipedia.org/wiki/Electro-magnetic_spectrum

The reason we see visible light the way we do, is partially because of the way the sun emits visible light with a signature spectrum, of varying wavelengths, mostly a byproduct of the fusion of hydrogen atoms into helium and the way the physiology of the human eye has evolved, with its system of rods and cones, sensitive to light and dark and colours, within what we know as the visible spectrum. Rods are sensitive to light and dark, but not colour. Cones are sensitive to colour and there appear to be three different kinds of them in most human eyes. People with only two different types of cones appear to suffer from colour blindness.

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html

People have been identified with four different kinds of cones, so called tetrachromats, they may see a somewhat different, more complex, colour spectrum.

https://en.wikipedia.org/wiki/Tetrachromacy

Various animals are also tetrachromats and can see different parts of the electromagnetic spectrum. Bees, for instance, appear to be able to see into the ultraviolet.

The reason colour pigments in paint don't mix true to pure visible light spectrum colours, is because the pigments used in paints are not really pure colours, but mixtures of various kinds. They don't emit light, but reflect it, or absorb it, in certain wavelengths.

Post of the week - awesome info!

 

[rynner2]

Rynner are you going to tell me that there's no pot of gold at the end, either?

Afraid so!

Everybody sees their own individual rainbow - where its end appears to be for me would not be the same place that somebody else sees. (In fact, my left eye sees a different rainbow from my right eye!) If all these rainbows had pots of gold, the world would be full of them!

The idea of a pot of gold at the end of the rainbow is just a poetic interpretation of an impossible dream or wishful thinking. If wishes were horses, then beggars would ride!

 

[rynner2]

And talking of colour vision, I may as well add this here:

Have we cured colour blindness? Scientist 'accidentally' creates glasses that allow people to see full spectrum
By Damien Gayle and Fiona Macrae
PUBLISHED: 14:52, 7 February 2013 | UPDATED: 07:42, 8 February 2013

They are the spectacles that could transform the vision of the colour blind.
Scientists have developed glasses with purple-tinged lenses that enhance reds and greens, allowing those with the most common form of the condition to see them properly.

One tester of the Oxy-Iso lenses, a British academic, has told how he ‘shivered with excitement’ after putting on the £190 glasses for the first time.
Dr Daniel Bor, of the University of Sussex, said: ‘The main thing I have problems with is when people use red and green on graphs in seminars and I can’t tell the difference between them.
‘And there’s my occasionally weird dress sense, which my wife puts me right on. But putting on the glasses for the first time was really quite an exciting moment. I was with my daughter in the gym and suddenly her lips stood out.
‘She was wearing a red-orange jumper and suddenly it stood out from the surroundings.’

The glasses, which were originally developed for medical use, are the brainchild of US scientist Mark Changizi.
The lenses filter out bands of light that interfere with the ability to distinguish various shades of red and green.
Dr Changizi, of Idaho firm 2AI Labs, said: ‘It makes it so they can suddenly see red-green differences in the world which were originally too small for them to notice.’

Wearing the glasses, Dr Bor managed to pass the colour blindness test used in schools around the world. However, they were not without their drawbacks.
He said: ‘My daughter’s baby monitor has a yellow light on it and normally I can see that. But with the glasses on, it was completely invisible.
‘Without the glasses, nothing is invisible. It was a bit disturbing that some things disappeared out of my vision.
‘I wouldn’t wear them all the time but if I was going to an art gallery or a flower show, I’d take them with me. I’d really welcome them then.’

The glasses only work for red-green colour blindness. This is the most common form and although rare in women, it affects up to 8 per cent of men.
On his blog, Professor Changizi said: 'Although we didn’t design our technology with colour-deficients specifically in mind, we weren’t too surprised that the Oxy-Iso may help with with red-green colour-deficiency.
'As I have argued in my research and my earlier book, Vision Revolution, our human variety of color vision evolved — above and beyond that found in other mammals — in order to sense these oxygenation variations, allowing us to sense colour-signals on the skin (including blushes, blanches, as well as sensing health).
'So the Oxy-Iso filter concentrates its enhancement exactly where red-green colour-blind folk are deficient.'

Daniel Bor, a researcher from the University of Sussex, said wearing the glasses enabled him to pass the commonly used test for colour blindness, the Ishihara Colour Test, in which patients are shown plates which feature a circle of dots.
Colour blindness sufferers are not able to make out numbers shown made up of dots of a different colour.

'When I first put one of them on, I got a shiver of excitement at how vibrant and red lips, clothes and other objects around me seemed,' Mr Bor said.

The glasses are already available. However, while they enhance perception of reds and greens, they hamper the ability to distinguish yellows and blues.

[VIDEO: Dr Mark Changizi explains the idea that lead to the invention of O2Amp Eyewear]

Read more: http://www.dailymail.co.uk/sciencetech/ ... z2KJEtZXCj

(Side-bar about colour blindness on page.)

 

[liveinabin]

There was a very interesting program on Radio 4 (isn't there always) about language and as part of this they talked about colour.
Now in English we have a name for pink, and perceive it as a different colour from red. In (I think) Italian they don't have a name for it and just call it light red. However they do have a name for light blue and see it as a different colour from blue. They talked to a woman who had grown up speaking both English and Italian in equal measure. When she was talking in English she could see pink and red as two different colours, but not the two blues. When talking in Italian she could see the opposite.
Please note that it may not be Italian, I honestly can't remember the language, but what is important is that her perception of colour changed depending on the language she spoke.

As for colour primaries, they are red, blue and yellow for paint and red, green and yellow for light.

 

[rynner2]

As for colour primaries, they are red, blue and yellow for paint and red, green and yellow for light.

Er, no, for light the primary colours are RGB. Yellow is a mixture of red and green.

(See my posts above for links.)

 

[Pietro_Mercurios]

And there was me thinking that green was a mixture of yellow and blue. :lol:

 

[rynner2]

And there was me thinking that green was a mixture of yellow and blue. :lol:

It is, if you're using pigments, such as the poster paints used in art class when I was at school.

It was Isaac Newton who, using prisms, first discovered that white light is a mixture of colours, the spectrum, and that these colours can be recombined to make white light again.

Primary colours are sets of colours that can be combined to make a useful range of colours. For human applications, three primary colours are usually used, since human colour vision is trichromatic.

For additive combination of colours, as in overlapping projected lights or in CRT displays, the primary colours normally used are red, green, and blue.

For subtractive combination of colours, as in mixing of pigments or dyes, such as in printing, the primaries normally used are cyan, magenta, and yellow,[1] though the set of red, yellow, blue is popular among artists.[2] See RGB colour model, CMYK colour model, and RYB colour model for more on these popular sets of primary colours.

http://en.wikipedia.org/wiki/Primary_color

(Lots of interesting info on that page! )

 

[amyasleigh]

Something here, extremely simplistic among all the scholarship, and probably quite untrue. Anyhow -- I've seen it suggested that an imaginary "indigo" band was included in the rainbow, between blue and violet, so as to allow the making of the mnemonic for the colours in their right order: the nonsense words -- running in opposite directions -- VIBGYOR and ROYGBIV.

 

[liveinabin]

As for colour primaries, they are red, blue and yellow for paint and red, green and yellow for light.

Er, no, for light the primary colours are RGB. Yellow is a mixture of red and green.

(See my posts above for links.)

You are quite right Rynner, I was confused.

 

[rynner2]

A fairly definitive article here:

QI: some quite interesting facts about rainbows
By Molly Oldfield and John Mitchinson
7:00AM BST 28 May 2013

The way I see it, if you want the rainbow, you gotta put up with the rain. Dolly Parton

Colours

Until the 17th century, no one had the faintest idea what a rainbow was, how it got there, or what it was made of. Homer thought that the rainbow had only one colour – purple. Xenophanes moved things on a bit and gave it three: purple, yellow-green, and red. In his Meteorologica, Aristotle insists: “The rainbow has three colours, and these three, and no others”; and this idea persisted until the Renaissance, when four colours (red, blue, green, yellow) were fixed upon.

By the time Isaac Newton turned his attention to them, pretty much everyone in the West agreed there were definitely five colours (red, yellow, green, blue, purple). To the average Chinese, even today, rainbows have five colours. And in the Baltic countries, for most of history people believed that rainbows had only two significant colours – red and blue. “Rainbow” in Estonian is vikerkaar.

It was Newton’s great rival, René Descartes (1596-1650), who first realised in 1637 that rainbows were caused by light from the sun being split into different colours by rain. But it is to Newton we owe the notion that rainbows consist of seven colours. Newton came up with this perception in 1666, holed up alone in his remote Lincolnshire farmhouse having escaped Cambridge, which was being ravaged by the plague.

The idea that the universe runs to the rule of seven goes back at least to Pythagoras – seven notes in the musical scale, seven days of the week, and, until the discovery of Uranus by the German-born, British-based William Herschel (the German for “rainbow” is Regenbogen) in 1781, seven planets – which is why Newton warmed to the idea. He added the colour indigo, along with orange, to give us a neat spectrum of seven colours.

Of course, there aren’t really seven colours in a rainbow, nor any particular number. Each “colour” shades imperceptibly into the next with no hard boundary other than those imposed by human observers of different cultures.

The Greeks and Romans thought a rainbow was the path made by Iris, the goddess of the rainbow, between heaven and earth, linking gods with humans. The iris of the eye is named after her, because of its colour. “Rainbow” in Latin is arcus iris or arcus pluvius, a “rainy arch”.

The Greeks used the word “iris” to describe any coloured circle, such as the “eye” of a peacock’s tail. The flower called iris gets its name from the Greek, as does the chemical iridium (Ir), compounds of which are highly coloured. Iris is also the root of “iridescent”.

Here comes the science part

A rainbow doesn’t actually exist, so it doesn’t really have an end where you can find a pot of gold. Optically speaking, it is just a distorted “virtual image” of the sun. Each raindrop acts as a tiny, imperfect mirror. When the sun is right behind you its light passes through the raindrops in front of you, reflects off their rear surface and bounces back at you. The light is refracted or “bent” slightly as it passes from the air into the water; and again as it bounces back into the air again. The different wavelengths that combine to make daylight are “bent” by different amounts (42º for the red end of the spectrum, a shade less for the violet). Each raindrop acts as both prism (refraction) and mirror (reflection).

The world’s longest-lasting (or longest-observed) rainbow was seen over Sheffield from 9am to 3pm on 14 March 1994.

A rainbow is a portion or arc (the Italian for “rainbow” is arcobaleno) of a circle whose centre is the shadow of your head. In some situations, for example skydiving, you can see the whole ring. From a mountaintop you might see a half-circle or more; usually, the 42° rule means the sun has to be fairly low in the sky before you can see a rainbow at all.

As well as the “primary arc” of a rainbow, it’s quite common to see a second bow outside it, with the spectrum reversed. These happen when light bounces around inside a raindrop more than once before making it out. Third and fourth and even multiple bows can sometimes be seen. So, occasionally, can “supernumerary” bows: extra bands of green and violet caused by complex interference patterns.

http://www.telegraph.co.uk/culture/qi/1 ... nbows.html

 

[amyasleigh]

I'd always had the notion -- from what I'd heard or read somewhere, no idea where -- that the "indigo" element in the rainbow was fictitious: not truly present in the spectrum, but added in so as to make a pronounceable aide-memoire word for the order of the colours; VIBGYOR or ROYGBIV. Clearly, there's a great deal more to it than that !

 

[IbisNibs]

Don't know if this will merit its own thread or not, since there is mention of these glasses for color blindness in the OP:

There are now commercially available glasses which don't fix color blindness, but augment color perception for people with red/green color deficiency. The glasses allow people to distinguish between these those colors to a much greater extent than they normally can.
This is the article that brought such glasses to my notice for the first time: https://www.sfgate.com/news/article/Video-of-Minnesota-boy-seeing-color-for-the-first-14864622.php
The headline is somewhat misleading.
Here's a more science focused article, but still has a slightly misleading headline, in that it sounds like the glasses don't help at all: https://www.eurekalert.org/pub_releases/2018-10/uog-dte102618.php
The glasses seem to work well enough to make a big difference for red/green color deficient people, but don't help fully color blind people.