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A slight elaboration about the way your eye works: The cones are not on-off affairs, and they are not limited to specific wavelengths. Each type of cone has a r

A slight elaboration about the way your eye works: The cones are not on-off affairs, and they are not limited to specific wavelengths. Each type of cone has a response curve, and these curves overlap (see e.g. the Wikipedia article about Cone cells: http://en.wikipedia.org/wiki/Cone_cell http://en.wikipedia.org/wiki/Cone_cell ). So different colors are not really "made up" by filling in the gaps between the wavelengths. Each color we see corresponds to a specific cone response pattern. So for example, 500 nm would lead to responses of (roughly) 0.3, 0.4, 0.1. This means the explanation here is slightly misleading, as it compares yellow (which is a color that does exist as a single wavelength) with magenta, which is by definition a mix of at least two wavelengths. You could say that magenta is a compound color, the interpretation by our brain of the simultaneous stimulation by at least two wavelengths (i.e. two or more cone response patterns). This means, of course, that magenta is far from the only color for which this is true. Any combination of at least two wavelengths is a compound color, and the interpretation of each of these combinations will not be found on the visible spectrum. So, interesting article, but a bit oversimplified, in my view.

fogleman 13y ago
Thank you, this makes more sense.
thaumasiotes 13y ago
> Any combination of at least two wavelengths is a compound color, and the interpretation of each of these combinations will not be found on the visible spectrum. Is it really impossible for the cone response to a compound color to match that of any single wavelength? There are yellow wavelengths, but we display yellow as a compound of red and green instead. That doesn't mean yellow can't be found on the visible spectrum.
- dietrichepp 13y ago
  > Is it really impossible for the cone response to a compound color to match that of any single wavelength? Yes. Look for a "chromaticity diagram" to see the colors we can perceive. It is a convex shape, like a truncated parabola, and the pure colors are on the edge of the parabola curve. Any time you mix two pure colors, you end up inside the parabola instead of on the edge. Conversely, any color on the inside of the parabola cannot be a pure wavelength and must be a compound color. There are a lot of colors we call "yellow". Some are pure colors and some are compound colors. The ones that your monitor display are compound colors that cannot be found on the spectrum. A decent monitor will represent brilliant yellow colors fairly well. This is due to the low curvature of the edge of the chromaticity diagram in the green-red range, which in turn can be ascribed to the similarity of the response curve for the L and M cones in the eye, compared to the S cones. However, brilliant turquoise and aqua colors won't show up on your monitor.
makomk 13y ago
Also, because of the overlap between the response curves of the different cone cells, there are colours that cannot be produced by any combination of frequencies of visible light but that the brain can still perceive: http://en.wikipedia.org/wiki/Impossible_colors http://en.wikipedia.org/wiki/Impossible_colors (Another side-effect of this: any display based around additive mixing of three colours, such as the computer display you're reading this on, cannot reproduce the full spectrum of colours available in the real world. Standard computer and TV displays are particularly limited in the range of greens and blues they can reproduce.)
- msutherl 13y ago
  re: the latter, there's a nice illusion for getting a feel for that: http://i.imgur.com/G3EoK.png http://i.imgur.com/G3EoK.png – an optical effect that allows you to see true cyan vs. computer display cyan
swayvil 13y ago
I make a study of funny colors. For example you can get weird vibrations via certain patterns of strobed color combinations and frequencies. This is an interesting study of such (warning! strobes!) : https://www.youtube.com/watch?v=dL0lNGXoP8E https://www.youtube.com/watch?v=dL0lNGXoP8E
- jeroen94704 13y ago
  Wow, anyone who can watch that without becoming epileptic is immune :). Interesting effects though.
- cepuxxx 13y ago
  this is beautiful
Steuard 13y ago
The really interesting thing, which I only learned a few years ago, is that there is actually a reason that we perceive colors in the "purple" range (including violet and magenta) as falling between red and blue on a "color wheel". Specifically, the "red" cones in our eyes have a minor secondary region of sensitivity that's way out in the blue-violet range. So violet light also partially stimulates our red receptors, making our brains interpret it as a mixture of red and blue. Here's one source: http://midimagic.sgc-hosting.com/huvision.htm http://midimagic.sgc-hosting.com/huvision.htm (I know I've seen other sources as well, but this phenomenon isn't discussed terribly often so I'm a little bit skeptical about it.)

fogleman 13y ago

Thank you, this makes more sense.

thaumasiotes 13y ago

> Any combination of at least two wavelengths is a compound color, and the interpretation of each of these combinations will not be found on the visible spectrum. Is it really impossible for the cone response to a compound color to match that of any single wavelength? There are yellow wavelengths, but we display yellow as a compound of red and green instead. That doesn't mean yellow can't be found on the visible spectrum.

dietrichepp 13y ago
> Is it really impossible for the cone response to a compound color to match that of any single wavelength? Yes. Look for a "chromaticity diagram" to see the colors we can perceive. It is a convex shape, like a truncated parabola, and the pure colors are on the edge of the parabola curve. Any time you mix two pure colors, you end up inside the parabola instead of on the edge. Conversely, any color on the inside of the parabola cannot be a pure wavelength and must be a compound color. There are a lot of colors we call "yellow". Some are pure colors and some are compound colors. The ones that your monitor display are compound colors that cannot be found on the spectrum. A decent monitor will represent brilliant yellow colors fairly well. This is due to the low curvature of the edge of the chromaticity diagram in the green-red range, which in turn can be ascribed to the similarity of the response curve for the L and M cones in the eye, compared to the S cones. However, brilliant turquoise and aqua colors won't show up on your monitor.

makomk 13y ago

Also, because of the overlap between the response curves of the different cone cells, there are colours that cannot be produced by any combination of frequencies of visible light but that the brain can still perceive: http://en.wikipedia.org/wiki/Impossible_colors http://en.wikipedia.org/wiki/Impossible_colors (Another side-effect of this: any display based around additive mixing of three colours, such as the computer display you're reading this on, cannot reproduce the full spectrum of colours available in the real world. Standard computer and TV displays are particularly limited in the range of greens and blues they can reproduce.)

msutherl 13y ago
re: the latter, there's a nice illusion for getting a feel for that: http://i.imgur.com/G3EoK.png http://i.imgur.com/G3EoK.png – an optical effect that allows you to see true cyan vs. computer display cyan

swayvil 13y ago

I make a study of funny colors. For example you can get weird vibrations via certain patterns of strobed color combinations and frequencies. This is an interesting study of such (warning! strobes!) : https://www.youtube.com/watch?v=dL0lNGXoP8E https://www.youtube.com/watch?v=dL0lNGXoP8E

jeroen94704 13y ago
Wow, anyone who can watch that without becoming epileptic is immune :). Interesting effects though.
cepuxxx 13y ago
this is beautiful

Steuard 13y ago

The really interesting thing, which I only learned a few years ago, is that there is actually a reason that we perceive colors in the "purple" range (including violet and magenta) as falling between red and blue on a "color wheel". Specifically, the "red" cones in our eyes have a minor secondary region of sensitivity that's way out in the blue-violet range. So violet light also partially stimulates our red receptors, making our brains interpret it as a mixture of red and blue. Here's one source: http://midimagic.sgc-hosting.com/huvision.htm http://midimagic.sgc-hosting.com/huvision.htm (I know I've seen other sources as well, but this phenomenon isn't discussed terribly often so I'm a little bit skeptical about it.)