Shouldn’t common sense dictate that either both be one, or both be the other?
In: 1934
Color from a light source is additive color. Color reflected from an object is subtractive color. They are basically opposites.
Color is how your brain interprets light wavelength. The brain, it turns out, is not an organ of logic or reason; it is an organ of survival, full of quirks and inconsistencies.
If you want to go down the rabbit hole of color theory, a nifty place to start is the concept of impossible colors. https://en.wikipedia.org/wiki/Impossible_color
The color “wheel” is basically an optical illusion that results from how the cells in our eyeballs respond to different wavelengths of light and how our brain interprets those signals.
In reality, light is in a linear spectrum that doesn’t wrap around with “red” at one end and “violet” at the other.
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Paint and light work differently.
If I’m mixing different colors of light together, the end result gets closer to white.
If I’m mixing different colors of paint together, the end result gets closer to black.
I think you are mixing up purple and violet, they look similar because that’s how transmission spectrum in conecells works out (red conecells have a secondary sensitivity peak at short wavelengths), but they are not the same. Violet is shortest wavelength visible light. Purple is white light minus green
https://www.pixelsham.com/wp-content/uploads/2016/03/sun_and_vision.jpg
In both cases, long and short cone cells get tickled, medium ones not so much.
At the time I’m posting this, nobody in the comments properly answered your question.
The trick is that the cells in your eyes that perceive the red wavelength are not working the way that you think.
They perceive mainly red at one end of the light spectrum, but are also slightly sensitive to the very opposite end of the spectrum, beyond blue, that’s why you can perceive indigo there, and your brain perceives it as a mix of blue with a bit of red.
It kinds of gives you the illusion that the spectrum “circles back” to itself.
The purple color is kind of artificially created by the brain.
This article explains it better than me: [https://www.zmescience.com/feature-post/natural-sciences/physics-articles/matter-and-energy/color-purple-non-spectral-feature/](https://www.zmescience.com/feature-post/natural-sciences/physics-articles/matter-and-energy/color-purple-non-spectral-feature/)
[https://cdn.zmescience.com/wp-content/uploads/2021/04/color-cones.png](https://cdn.zmescience.com/wp-content/uploads/2021/04/color-cones.png)
Purple is not one of the colors on the rainbow. It’s not on the electromagnetic spectrum. Purple is a mixture of red light and blue light; it comes from 2 places on the electromagnetic spectrum. Violet looks purple to the human eye and it is one of the rainbow colors. Mixing paint is different from mixing light sources.
People see colors because of the cone cells in the eye. There are 3 types of cone cells, that are most sensitive to red, green and blue light respectively. The color that you see is determined by the relative strength of the signals that these cone cells give to your brain. When both blue and red signals are strong, you perceive the color as purple. That’s why you can add red and blue lights to get purple. The reason that the short end of the electromagnetic spectrum appears violet/purple is that the blue cone cells contribute a little bit to the red signals that your brain receives, in the absence of a green signal. (I am simplifying things here, you’ll need to drill deeper into Opponent Process to get the full picture).
Relevant Wikipedia links:
https://en.wikipedia.org/wiki/Violet_(color)#Optics
https://en.wikipedia.org/wiki/Opponent_process
Because purple doesn’t actually exist as a wavelength. It’s the brain’s interpretation of red and blue in the absence of green.
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