Why magenta doesn't appear in the rainbow


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All colour is perception created by the brain. The eyes provide raw data. If you are perceiving something you want to call magenta, then go ahead and call it a colour.


Color theory is a lot more complex then that.

Magenta is a color, in fact it is one of the primary colors of subtractive color theory.

It depends if you are discussing additive (light) or subtractive (pigment) color theory.

Additive color theory focuses on the light, and the light the eye perceives are Red Green and Blue photons, which is why TV’s and other light projectors mix RGB. All colors can be made from mixing Red Blue and Green light.

Subtractive color theory focuses on the “color” of the object itself which is what determines what is absorbed and what is reflected. In pigments all colors can be made from mixing Cyan Yellow and Magenta pigments (CMY). This is why inkjet printers can make all the colors using Cyan Yellow and Magenta ink cartridges. They often include a Black cartridge as well to get a “true black” (K) and save the others from the excess of black printing associated with text (CMYK)

You cannot make all colors by mixing CMY light, nor can you make all colors by mixing RGB pigments.

Color theory is something incredibly fascinating to study, and people who haven’t studied it thoroughly tend to get hung up on one side or the other and argue the that opposite is incorrect, when really they are inseparable.


“A ship loaded with red paint ran into a ship loaded with purple paint this afternoon. At last report, both crews were still marooned.”


My first response to this was “Wait, it doesn’t? I thought violet and indigo were official ‘rainbow’ colours?”

Then I watched the video, and it was pretty much this:


I have a friend who insists that the atmosphere isn’t blue, because [explanation reduced to noise through having heard it so many times, but the words “Rayleigh scattering” are in there somewhere] and so the colour isn’t produced in the regular way. The sky is blue, but the air isn’t. What happens if you take the air away and replace it with, say, chlorine, I ask? The sky becomes green, he says, because chlorine is green. But oxygen-nitrogen isn’t blue, I say? Weren’t you listening, he asks? Then he goes into the explanation again.

So tell me again how magenta isn’t a colour, despite the fact that I can point to it in RGB, HSL, CMYK and Pantone. I need to zone out for a bit while I do some photoshopping.


I came here to say: ‘if magenta isn’t a colour, then yellow and cyan aren’t colours either.’

/I work with this stuff all day long.


Except there totally is a purple section of rainbows, right? Definitely not magenta, but a nice deep purple/violet after the blue. So what is getting added or removed at that point, as the wavelength moves out of the visible spectrum?


“…and maybe some unnamed creature
stayed awake all night in the
midst of a thousand miles of colour
just to see what it felt like
to have all the blue-purple there was
explode in his brain
and alter both present and future…”

From Al Purdy’s In the Early Cretaceous


He’s not even wrong. The color we call “violet” from the rainbow does exactly the same thing that he says “magenta” does. It stimulates the red and blue cone cells in your retina, but not the green cone cells. Even though it’s not “in between” blue and red. You’ll also note that the pure frequency of “violet” in the rainbow does not contain any green wavelengths. Thus the lack of green in it. Just like “magenta.”


Such as the guy who very earnestly tried to convince me that clearly laser printers must print in RGB because lasers are just light, right?


Is it just me who wants to know - Where do you get hold of the colored torches?


So the red cones respond to wavelengths around the color red and to wavelengths shorter than blue?


It is a colour. It’s just not a spectral colour.

(And your “red”, “green” and “blue” cones are actually most sensitive to orange-yellow, yellow-green, and blue-violet. But using red, green and blue in TVs and computer displays gives a better spread of colours.)


It just might be the language that is inadequate and not the physical world.


But that’s not quite the same thing, is it? Because you can point to a wavelength (indeed, many wavelengths) and say “this is yellow light”, and similarly for cyan; but there’s no wavelength you can point to and say “this is magenta light”.


Yes, red and blue cones both fire when you look at violet rainbow light. Even though the wavelength is shorter than blue, the red cones do actually fire. They are not limited to only firing on the longer red wavelength.


Not really. You’re arguing semantics. There is a wavelength of light that produces the sensation of yellow. There is no wavelength of light that produces the sensation of magenta - you can only do it by mixing two different wavelengths. (You can also produce a sensation of yellow by mixing two different wavelengths, but this will only work if the viewer is a trichromat, which most of us are)

When he says “color” he means something like “a pure wavelength of visible light”, when you say color, you’re talking about something like the specific sensations we get. You’re just talking past each other.


There is indeed a spectral color that stmulates blue and red cones. We use the word “violet” for it.


Violet is not magenta. The mechanism is similar, but the values are not.