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Comment by Rygian | Hacker News Reader

The interesting bit here, for me, is that the eyes perceive _as almost the same color_ the yellow in a yellow lemon, and the yellow made by the combination of green and blue from a screen. I find that convergence fascinating.

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That is because we also can't actually directly perceive the yellow from that lemon, i.e. we don't possess cones that have their max sensitivity at 570 nm (yellow). Instead yellow is created in our brain by combining the data from the M and L cones: If both signal at about equal intensity, our brain calculates that to be yellow. So the perceived yellow can actually be 570 nm, or 540 nm (yellow-green) plus 600 nm (orange) or similar. Only if the distance between both wavelengths is too high this stops working.

These two different yet same yellows have a fancy name too: metamers. [1] I think it’s super interesting too, and you can even create metamers out of non-metamers using the right light sources. As a trichromat subject to the same metamers as most humans, I want to know what it feels like to be a tetrachromat who can see the differences between colors I can’t tell apart. Or a bi/mono-chromat (aka color blind) where metamers really start to stack up.

https://en.wikipedia.org/wiki/Metamerism_(color)

  red + green = yellow
  green + blue = cyan

Thanks, you're right! I typed without thinking.

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