# The impossible colour: blueish-yellow



## qubit (Sep 6, 2018)

This fascinating video from The Action Lab shows why we can't perceive it and one other impossible colour.

However, there's a simple trick he uses in the video that allows some people to see it and I think it worked for me.


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## MrGenius (Sep 6, 2018)

I haven't watched the video yet. But I can clearly see the word "Forbidden" where the red arrow is pointing to in the thumbnail.

EDIT: I watched the vid and did the experiment. I saw it. I want to call it bluish yellow though. It seems more yellow than blue to me. I would also describe it as kind of a greyish green. Weird.


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## FordGT90Concept (Sep 6, 2018)

Color Gamut:





See how small the yellow region is and how when you connect yellow and blue, you get white.  Makes sense.


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## Caring1 (Sep 7, 2018)

I can see it in the still of that video, even without watching it.


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## qubit (Sep 7, 2018)

Caring1 said:


> I can see it in the still of that video, even without watching it.


Did you cross your eyes? I couldn't get anywhere near having the crosses meet, but the slim overlap down the middle was enough to see it. It was unstable though.


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## Nuckles56 (Sep 7, 2018)

I couldn't manage to see it, I tried and tried to do so.


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## qubit (Sep 7, 2018)

Nuckles56 said:


> I couldn't manage to see it, I tried and tried to do so.


Did you cross your eyes and have the areas overlap? Also, varying your viewing distance and relaxing as much as possible might help.

Even though I think I saw it, it wasn't stable so I didn't see a merged colour the whole time. Instead it tended to flip flop between blue and yellow like the video said it could. Finally, it wasn't too comfortable keeping my eyes crossed!


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## hat (Sep 7, 2018)

I thought blue and yellow made green?


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## StrayKAT (Sep 7, 2018)

What..? I made this with play-doh as a kid all the time 

Technically, it makes up green, but it seems like many materials make it turn out as teal/cyan.


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## robot zombie (Sep 7, 2018)

hat said:


> I thought blue and yellow made green?


That's the difference between light reflected off of pigments/objects and perceived light. Color is subtractive when it comes to objects reflecting/absorbing light. Something that's blue only reflects blue light and something that's yellow only reflects yellow light. They absorb everything else. The remaining wavelength reflected by a material that is subtracting everything but yellow and blue light ends up falling in the middle of those two wavelengths, which results in an object that predominantly reflects green light. You're not seeing yellow light and blue light mixed together. The light reflected is actually green. By mixing the two pigments with different reflective properties, you've changed those properties. Subtract a little extra yellow and a little blue, and the green light in the middle comes out more prominently than any other color, because less green light is being subtracted than that of any other color. So what you get is a darker green shade.

When dealing strictly with light hitting your eyes, you're looking at additive color. It has to do with how our eyes react to light and how our brains interpret it. Basically when only blue and yellow light hit our eyes, they cancel out due to the way our vision system works. Having two wavelengths (yellow and blue) hit your eyes at the same time is interpreted differently than seeing actual green light reflected by an object that absorbs every wavelength except for the ones between yellow and blue.

To make it more confusing, the positioning relative to each other on the visual spectrum causes different combinations of lights to be interpreted differently. Mixing red and green light results in a light that appears yellow. But actually the wavelengths of light hitting your eyes are that of red and green, not yellow. It's not a property of light. Our eyes see two different colored lights and our brains make one color out of it, depending on how they relate to eachother. Colors next to each other on the gamut combine to make other colors, while colors directly opposite to each other cancel out. Sort of like how two equal + and - charges result in a voltage potential of 0.

Say you were sitting in a wagon. Two equally strong people push on the front and the back. In this case, you go nowhere. While if you have one of those people push at a slight angle, you will move slightly in that direction. Does that make any sense? I feel like maybe it doesn't. It's not easy to explain. More just one of those things that's easy to know, but hard to comprehend... ...like the distance from the earth to the sun.

It's very strange and counter-intuitive, but I'm pretty sure that's the gist of it.


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## RichF (Sep 7, 2018)

The eye can see three colors: blue, red, and green.

All the colors our brains perceive come from those three.

Additive (e.g. computer screen) and subtractive (e.g. printer, paint) mixing are different.

Red-green is another forbidden color, to go with blue-yellow.












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

In addition to impossible colors, there are non-spectral colors, like magenta. This is why there is no magenta in a rainbow (or light separated by a prism).

Stars are also interesting. There are no violet stars, no magenta ones, and no truly green ones.

https://www.livescience.com/34469-purple-stars-green-stars-star-colors.html


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## Nuckles56 (Sep 7, 2018)

qubit said:


> Did you cross your eyes and have the areas overlap? Also, varying your viewing distance and relaxing as much as possible might help.
> 
> Even though I think I saw it, it wasn't stable so I didn't see a merged colour the whole time. Instead it tended to flip flop between blue and yellow like the video said it could. Finally, it wasn't too comfortable keeping my eyes crossed!


I did both those things and nothing ended up happening


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## robot zombie (Sep 7, 2018)

RichF said:


> Red-green is another forbidden color, to go with blue-yellow.


That's never made sense to me. I mean, I know it's just what they're called, but logically shouldn't they be blue-yellow, red-cyan, and magenta-green? That's all a forbidden color really is, right? Just complimentary colors cancelling out. It's confusing when you consider that red and green light do appear yellow, and yet any of the combinations I listed will appear colorless.  And if yellow-blue and red-green are forbidden, why isn't there a 3rd forbidden color? Shouldn't there be 3 possible impossible combos if there are 3 additive primaries and three different colors of our eyes can see? And if it's related to primary colors/the 3 types of cone cells, why is yellow involved at all? In that case the only real one would be red/green... ...but that still makes yellow. Or maybe is it tied to the physical side of how we detect light? Differences in the response or density of different cones?

I know I'm missing something there...


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## RichF (Sep 7, 2018)

robot zombie said:


> That's never made sense to me. I mean, I know it's just what they're called, but logically shouldn't they be blue-yellow, red-cyan, and magenta-green?


We have no cones for magenta, nor cyan.

Yellow is tricky because we don't have any cones for it, either.


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## robot zombie (Sep 7, 2018)

RichF said:


> Yellow is tricky because we don't have any cones for it, either.


Yeah, that's what gets me. I don't see the logic to it. Unless it's a physical anomaly of the human vision system it doesn't make sense. Logically it would make sense that red-green would be one, since we have cones for those. But that appears yellow, which would seem to disqualify it, but it doesn't. Yellow-blue does appear colorless and yet we don't have cones for yellow. So if we want to call that a forbidden color, than other combinations of primary/secondary colors should logically be included.

I guess what I'm not seeing is the function of the designation. What distinguishes yellow-blue as a forbidden color that doesn't also imply that say, magenta-green is one as well. Why are these forbidden colors so waffley? Somebody's gotta know.


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## johnspack (Sep 7, 2018)

Wish I could see it,  but because of our sucky medical system,  I'm mostly blind in one eye due to corneal edema.  Canada has awesome medical services!


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## RichF (Sep 7, 2018)

robot zombie said:


> Yeah, that's what gets me. I don't see the logic to it. Unless it's a physical anomaly of the human vision system it doesn't make sense. Logically it would make sense that red-green would be one, since we have cones for those. But that appears yellow, which would seem to disqualify it, but it doesn't. Yellow-blue does appear colorless and yet we don't have cones for yellow. So if we want to call that a forbidden color, than other combinations of primary/secondary colors should logically be included.
> 
> I guess what I'm not seeing is the function of the designation. What distinguishes yellow-blue as a forbidden color that doesn't also imply that say, magenta-green is one as well.


Well, one clue may be the distance between red and green and between yellow and blue on the spectrum shown in the rod & cone picture I posted.

Notice how there is roughly the same distance between the colors in the pairs (roughly the same distance between red and green and between yellow and blue). The distance between red and green is a bit larger but the wavelengths of the various colors also are a factor, with blue being more energetic than red.



			
				hyperphysics said:
			
		

> By population, about 64% of the cones are red-sensitive, about 32% green sensitive, and about 2% are blue sensitive. The "blue" cones have the highest sensitivity and are mostly found outside the fovea. The shapes of the curves are obtained by measurement of the absorption by the cones, but the relative heights for the three types are set equal for lack of detailed data. There are fewer blue cones, but the blue sensitivity is comparable to the others, so there must be some boosting mechanism.
> 
> When light strikes a cone, it interacts with a visual pigment which consists of a protein called opsin and a small molecule called a chromophore which in humans is a derivative of vitamin A. Three different kinds of opsins respond to short, medium and long wavelengths of light and lead to the three response curves. For a person to see an object in color, at least two kinds of cones must be triggered, and the perceived color is based on the relative level of excitation of the different cones.


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## robot zombie (Sep 7, 2018)

RichF said:


> Well, one clue may be the distance between red and green and between yellow and blue on the spectrum shown in the rod & cone picture I posted.
> 
> Notice how there is roughly the same distance between the colors in the pairs (roughly the same distance between red and green and between yellow and blue). The distance between red and green is a bit larger but the wavelengths of the various colors also are a factor, with blue being more energetic than red. Our eyes also perceive green with greater intensity than the other two colors we have cones for.


Mmm, that would make sense. I figured it might be something like that. Differences in actually sensitivity at different ends of the spectrum.


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## DeathtoGnomes (Sep 7, 2018)

Red Green was a great TV show. 

Feel the rainbow. Some people can feel colors, thats impressive.


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## Arjai (Sep 7, 2018)

I not only feel colors, my feelings make me see colors. Music can also bring colors. Basically, strong emotions have colors, for me. Wanna know what is really weird, I am color blind, I cannot differentiate red and green. The biggest problem I have had was driving cross country, there are places that have Stop Lights positioned horizontally, Unless I saw the light change, because of the yellow light coming on, I was unsure if it was a red or green light! However, my mind's eye is not color blind and I do see green and red, vividly, when emotionally charged.

I am unsure if it is impressive. I also don't know any different. I didn't know I was different until I was in my teens, that was also when I stopped talking about it. I was in my 30's before I even knew what it was, I heard a radio show interview with a musician, who was talking about his music being colors. Synesthesia, is what it is called. It's funny when I read things about it. For instance, I am good, very good, at Math, or was, or can be, but, I do not associate colors to it, or to words, rather, maybe some words, not really sure. Haven't really bothered to write them down.

I just do me, and try not to stand out, too much.  I also try hard not to reveal it to people, when it is happening, even though that can be difficult, at times.

Anyway, back to our regularly scheduled programs.

Punch Drunk Love, is the only movie that had scenes that were anything like what I feel like, sometimes. If you are familiar w/ that movie, there are moments of color, that had to be made by someone with Sensythesia.


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## Caring1 (Sep 7, 2018)

The only colours I have difficulty with is red and blue.
Red writing on a blue background or vice versa is a headache for me, it instantly blurs.


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