this post was submitted on 26 Jul 2023
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Colourblind isn't the complete absense of colour, e.g. everything looks black and white. With deuteranomaly, you are the actual textbook definition of colourblindness... There are different levels of it, but all can still perceive colour - it's just whether the difference in colour of the spectrum is detected correctly.
Deuteranomaly (/ie) is the reduction in reactivity of the red-colour receptors. That means your perception of orange/red/brown is less than those with normal vision.
For those with normal vision, this is a great chart. But, if you're colourblind, it'll be more confusing for you, sorry!
So everyone can see a form of blue, most being royal blue? That's super interesting because there's a saying in art, "If you can't make it good, make it blue."
Why does the chart not include purple?
If I were to guess, it might be because purple isn't a wavelength of light, it's like a glitch in how we perceive light with the two cones opposite to each other in the spectrum being stimulated at the same time without the middle one.
For any practical purposes in every day life, purple is a color, it just doesn't exist outside our perception.
Suddenly, the 40k meme of purple orkz not existing gets a whole new meaning
I've actually gone really deep on this and the graph they're shows the mechanism at work. "Purple" strictly doesn't exist, you're right, but also wrong. Violet activates essentially the same receptors, "blue cones" in the retina are mainly only sensitive to blue/violet, but if you look at it, the "red cones" actually have an uptick at the extreme of blue (into violet), so when just blue is activated, we see blue, but when we see red+blue, we see it as violet/purple, because if our eyes were seeing actual violet, that's what would be activated.
Purple as red+blue, doesn't exist, it's literally a hack to trick our brain into thinking it's seeing Violet, when it is not.
EDIT: this is a far better explanation than anything I could come up with, and demonstrates the phenomenon. https://jakubmarian.com/difference-between-violet-and-purple/
It does include purple, it's a little bit before the 400nm mark.