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Actually, the answer turns out to be pretty interesting.
The short version is that what colors are considered "distinct" are heavily influenced by culture and Newton, from whom we get ROYGBIV, came from a culture which valued the dye called "indego."
Edit: It also seems Newton thought the number 7 had cosmic significance and thought there ought to be 7 colors.
More info in this short video: https://www.youtube.com/watch?v=bf7WT6TLy8s
Well it was the 1600s and he was a natural philosopher. Back in those days, all sorts of weird stuff ended up in the books because it fit a certain philosophy. Our modern understanding of empirical science is a relatively new idea.
I'm confused...
Doesn't a rainbow contain all colours by definition?
It doesn't contain pink or brown. Some of the colours we see are how we register a mixture of light frequencies, whereas each point in the rainbow is just a single frequency.
What a phantastic thread!
We have had linguistics, sociology, physics and now biology in the form of colour perception so far.
Cross domain discussions are great! :-)
This is incredibly incorrect. While many colors that are additive are combinations, those combinations are simply approximations of the single wavelength true color. All colors are on a spectrum of hue, luminance (brightness) and intensity (saturation).
Pink is red with high luminance and high intensity, and brown is orange with low luminance and mid-high intensity
Nope. A whole bunch of colors do not correspond to any wavelength of light. This includes purple.
Among some of the colors that are not spectral colors are:
Grayscale (achromatic) colors, such as white, gray, and black. Any color obtained by mixing a gray-scale color and another color (either spectral or not), such as pink (a mixture of a reddish color and white), or brown (a mixture of orange and black or gray). Violet-red colors, which in color theory include line of purples colors (such as, approximately, magenta and rose), and other variations of purple and red. Impossible colors, which cannot be seen under normal viewing of light, such as over-saturated colors or colors that are seemingly brighter than white. Metallic colors which reflect light by effect.
https://en.wikipedia.org/wiki/Spectral_color#Extra-spectral_colors
Pink can also be described as a reddish hue with high brightness and low saturation. But saturation is a matter of how strongly one frequency is emphasized compared to other frequencies. So colors with low saturation contain mixtures of frequencies, but each point in the rainbow, when there's no other source of light present, is only a single frequency. This is why the rainbow doesn't contain any desaturated colors like pink. Brown, I admit, can be just dark orange.
Well yes, but the differentiation of colors varies by, believe it or not, culture! For example, the Japanese word for blue, 青 (ao) was used both (depending on context) for what we would call blue and green, and it wasn’t until modern times that a new word, 緑 (midori) started being used to explicitly define what we might call green. Even now, their ‘green’ traffic lights would be described as blue in other cultures. My apologies for the euro-centric over-simplification, but here’s a great article to elaborate further: https://cotoacademy.com/japanese-color-blue-green-aoi-midori-青い-みどり/
Interesting point.
And I am a little bit with the Japanese in this regard. At least my GF always complains that I am unable to correctly distinguish between green and blue ;-)
There's a difference between linguistic simplicity and color blindness.
Well in my case it's more about where to draw the line between blue and green.
I can differentiate the colours but just still call things blue that my GF (and most of the rest of the world, apart from Japanese and the german dialect I grew up with as it seems) already calls green.
This is a running joke in my house. My daughters like to wear a lot of blue/green shirts. Apparently I always guess it wrong.
Finally, I am not the only one! Feels good.
Actually....
There is no purple light.
Kinda.
Video explaining it in detail: https://youtu.be/CoLQF3cfxv0
Several colors we can perceive only exist as a specific mixture of wavelengths. And purple (coincidentally for this thread) is one such - white light contains it, sure, but, you can't isolate it to a specific single band, like you can isolate cyan or yellow. So, no, rainbows can not have purple in them.
I disagree. That color he keeps talking about is magenta, there is no magenta light. I see purple in the rainbow, but not magenta.
You would be half correct. Magenta is impossible "in the real world". It obviously exists on your computer screen due to its ability to shoot colored light into your eyeballs
Well yeah. I guess my question should be “why do we learn indigo and violet when we learn about the rainbow”. It’s more cultural
Yes, exactly.
E.g. in Germany I don't have heard anyone using Indigo and Purpur as major colours but only in combination with blue : "Purpurblau" and "Indigoblau" describing certain forms of blue.
So only blue and violet in german rainbows. And ultraviolet because most of us are more engineer than poet nowadays ;-)
You'd think so but colours are weird. Some of the ones we see aren't ones that actually exist, they're invented by our brains. Magenta for example doesn't exist, there is no wavelength for it and because of the way our eyes detect light it should really be a shade of green. But our brain doesn't like that and invents a brand new colour instead.
In Czech it's red, orange, yellow, green, turquoise, blue, violet/purple (we have the same word for both).
Edit: Violent -> Violet
Violent purple sounds like a band you'd find in an underground club in Berlin.
big rainbow is powerful.
Because purple is a combination of wavelengths and the rainbow has only has the single wavelengths. It also missing “lighter” colors like pink and “darker” like brown
???
Purple is not a combination of wavelengths, it is a single one. And pink and brown are lighter/darker versions of other colors. Pink being light red, and brown being dark orange.
Depends on how you define purple. If violet is close enough to purple for you then that "purple" would be a single spectral color, a single or continuous set of wavelengths. If it's just a little more like magenta it would be a non-spectral color. A combo of red and blue light.
Plenty of non-spectral colors. Most things we see are non-spectral colors. Single pigments give off multiple wavelengths. Most things have combos of pigments on top of that. Emission spectra are multiple wavelengths.
Purple is often defined as the color we perceive when something reflects blue and red light, whereas violet is a specific region of the light spectrum between blue and ultraviolet.
Indigo, the purple made as a combination of red and blue does not exist on a rainbow in the classical sense.
The rainbow is the electromagnetic spectrum that our eyes can detect and our brain interprets these waves as colours. Essentially our brain can detect 3 colours separately, red, green and blue.
Light does not exist as a single colour in reality but instead is a lot of different colours hitting our eyes at almost the same time, which is why you can get a rainbow out of sunlight, but if you put a red light into a prism, you will only get red light out, or if you put other household lights into the same prism, the rainbow would be different, colours would be less intense or missing. That's why light under different sources feel cool or warm but when you look at their spectrum as shown in the attached picture, they're almost all one colour.
Your brain is able to interpret these colours extremely well with context and is the source of a lot of optical illusions.
So when you see a combination of red and blue together, your brain interprets it as indigo purple and is why it is different from a pure violet wavelength.
Also, as common as brown is in the world, it doesn't exist on the rainbow, because it's a dark orange colour and its weird to think about it that way.
Brown is such a weird color
The rainbow is white light that has been split into its component parts. So the only colors that appear on the rainbow are made from a single wavelength. The missing shades of purples are made from a mixture of both high and low frequency light.
RGB color is a fair approximation of human color vision. Your screen's Red, Green, and Blue, components are designed to match the 3 cone cells of the human eye.
If you compare a real rainbow to the RGB rainbow in the color picker in your favorite graphics software, you'll likely notice extra colors. Unlike a real rainbow, the RGB rainbow has shades after blue, and it comes back around to red. Real rainbows do not do this.
That's because purple, and magenta and fuchsia and other similar shades are made from both high and low frequency light. Therefore they cannot appear on the rainbow.
I just wanted to add this link to xkcd’s survey results about color names because it’s fun and possibly relevant.
Because ROY G BIV is much easier to remember and say.
I have been trolling people for years with passionate wat-too-serious arguments that the rainbow is ROY G BAP for blue and purple.
in part what color each words refers to changes over time as all languages change.