I always learned “ROYGBIV” as the colors of the rainbow. Red, orange, yellow, blue, indigo, violet.

What’s up with the last two? Isn’t indigo basically just dark blue? Why is it violet and not purple? Can’t it just be “ROYGBP”?

    • floofloof@lemmy.ca
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      1 year ago

      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.

      • Rexelpitlum@discuss.tchncs.de
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        1 year ago

        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! :-)

      • Dr Cog@mander.xyz
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        1 year ago

        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

        • TonyTonyChopper@mander.xyz
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          1 year ago

          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

        • floofloof@lemmy.ca
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          1 year ago

          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.

    • Dewbs84@lemmy.fmhy.ml
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      1 year ago

      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/

    • DrQuint@lemmy.world
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      1 year ago

      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.

      • FiskFisk33@lemmy.world
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        1 year ago

        I disagree. That color he keeps talking about is magenta, there is no magenta light. I see purple in the rainbow, but not magenta.

        • Dr Cog@mander.xyz
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          1 year ago

          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

    • mookulator@wirebase.orgOP
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      1 year ago

      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

      • Rexelpitlum@discuss.tchncs.de
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        1 year ago

        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 ;-)

    • Thassar@lemmy.blahaj.zone
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      1 year ago

      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.

  • Rikudou_Sage@lemmings.world
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    1 year ago

    In Czech it’s red, orange, yellow, green, turquoise, blue, violet/purple (we have the same word for both).

    Edit: Violent -> Violet

  • lefixxx@lemmy.world
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    1 year ago

    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

    • Dr Cog@mander.xyz
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      1 year ago

      ???

      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.

      • KaJashey@lemmy.world
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        1 year ago

        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.

      • beefcat@lemmy.world
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        1 year ago

        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.

  • smithjoe1@lemmy.world
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    1 year ago

    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.

    • snoopen@lemmy.world
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      Essentially our brain can detect 3 colours separately, red, green and blue.

      Do you have a source for this? I’m pretty sure our brains can detect any arbitrary wavelength within a range. The red green blue thing just happens to be the three colours we can mix to emulate most (but not all) of the frequencies we can detect.

      • DKP@lemmy.world
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        1 year ago

        There are 3 types of cones in the human eye, which reactive to different bands of the spectrum. They peak at approximately red, blue, and green. Our brains are good at combining that information to make it appear seamless. Colorblindness is generally a genetic defect in the production of one or more of those type of cones. https://askabiologist.asu.edu/rods-and-cones

  • Hildegarde@lemmy.world
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    1 year ago

    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.

  • surfrock66@lemmy.world
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    1 year ago

    I have been trolling people for years with passionate wat-too-serious arguments that the rainbow is ROY G BAP for blue and purple.

      • RightHandOfIkaros@lemmy.world
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        1 year ago

        Indigo color is created by mixing more parts of Blue than Red.

        Violet color is created by mixing more parts of Red than Blue.

        Purple is created when two wavelengths are visible at the same time, between Red and Blue. At the same time, Violet colors border on Red, and Indigo colors border on blue.

        Therefore, Purple is a color inbetween Violet and Indigo.