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Comment by ccppurcell | Hacker News Reader

This article gets the colours wrong. Do the red figure example for yourself. If you do it correctly you will clearly see cyan, which is the opposite of red in RGB . It has nothing to do with the "primary colours" of blue and yellow mixing. Basic science facepalm from Smithsonian it seems.

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I think there is more to it than a simple "facepalm". In the modern RGB model, green and blue are primary colors, and mixed together, you get cyan, the opposite of red. So the explanation is generally correct, the only thing wrong is that yellow is considered a primary color instead of green.

But look here, and remember the book was published in 1864: https://en.wikipedia.org/wiki/Complementary_colors

Look at the color wheels of that period and earlier, especially this one: https://commons.wikimedia.org/wiki/File:Color_star-en_(terti...

And you see that red is the opposite of green. Why not cyan? I don't know. I guess cyan simply wasn't a well recognized color back then, maybe cyan was called green (a blueish green). Maybe our perception changed with the availability of modern pigments and screens.

As for the color you see when trying the illusion, it is even more interesting because it is actually an impossible color! [1] It doesn't correspond to a wavelength of light or a combination thereof, you can only perceive it through an illusion like this one. If we follow the Wikipedia article, and considering that the afterimage appears on a dark background that would be "stygian cyan". Spooky! Again, the theory was probably unknown in 1864.

[1] https://en.wikipedia.org/wiki/Impossible_color

> Why not cyan? I don't know.

Because tradition, and the pigments they used. Red, yellow, blue worked great.

https://en.wikipedia.org/wiki/Primary_color

It's a common mistake thanks to people learning in school that the "primary colors" are red, yellow and blue but the explanation is mostly right otherwise: you see cyan because it's a mix of blue and green, i.e. what you get when you subtract red from white light.

Of course human visual perception is a bit more complex than that but the primary mistake here is mixing up RGB and RYB. Quirks of color perception then result in referring to the resulting color as "green" when it clearly contains blue.

Also, the whole idea that "green" and "blue" are different things is culturally determined -- many languages either use one word that contains the shades English speakers call "blue" and "green" or did so historically before introducing separate words after they were influenced by English or other languages that make the distinction.

https://en.wikipedia.org/wiki/Blue%E2%80%93green_distinction...

Doesn't the eye have distinct perceptors for green and blue, or am I missing something?

No. There are three types of cone cells (S, M, and L) that are most responsive to various wavelengths of light, but as the picture shows, most "colors" are within the high and low ranges of more than one type of cone.

https://en.wikipedia.org/wiki/Cone_cell

For those who downvoted this, did you read the wikipedia entry? Seriously, the idea that many languages don't make a blue/green distinction is a fact.

The classic example is Homer's "Wine-dark sea", but it gets a lot more complicated than that https://en.wikipedia.org/wiki/Linguistic_relativity_and_the_...

The title is also wrong. It's more "... to show that mediums could fool you easily."

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