This seems to be the original picture , I’m still trying to figure out whether it’s a part of the human body…:
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I think it might be a number in a different language
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I saw the 5 instantly because I’m not colour blind but cannot see a number in the second image. A search on it produces this. See the caption below…
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I’m glad I bothered to read to the end of this thread because it reassured me I’m not going bonkers!
When I first looked at the pic in the Opening Post last night, I could see an odd pattern but I couldn’t see any number.
Today, I looked at the pic again and clearly saw the 5.
I thought my eyes or my mind must have been playing tricks on me last night because it looked like a completely different picture to the one I saw today.
It wasn’t until I read down the thread that I realised it really was a different picture!
Phew! I’m glad to know that! 
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Oh no I saw “7779311” 
I think that I need to see the doctor…
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Got number 5.
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Welcome to the forum Poppet. I hope you stick around…
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All I can see is a mouldy pizza! 
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First and second test images with the colour removed…
Hello Poppet 
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Is there a conclusion about that? The first image looks more uniform. I couldn’t guess that a 5 shows out of that. The second image has darker and bigger spots in places. I can see some of what I saw in the color image.
Is the conclusion that color verification doesn’t depend on shades of color?
It shows how a totally colourblind person would see those images. Harder to figure out is why they test works. Why, when the colour is removed, the number cannot be seen.
I think it is something to do with luminance or brightness values. If the small circles all fall within a certain level of brightness, it will need a colour to define any shape or number contained within them. If the colour is taken away, the eye won’t detect the number sitting in the background.
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I don’t know much about it, but I don’t think so. I think that colorblind people can see brightness values. That’s why the first picture looks flat to people who can see colors. If there were shades of gray, I think colorblind people could see it.
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Yes they can see the shades of grey but the difference in the shades isn’t starkly different. If the circles making up the number were darker or lighter, the number would start to stand out from the background …or the other way around where the number was made up of lighter darker circles and the background of lighter ones.
It comes down to how the eye works I suppose, Generally speaking, it’s the cones that determine colour values and the rods that see brightness levels. No expert either but if the cones are not responsive enough (or not at all), the eye only has the rods to depend on for sight. Since those circles may fall with similar levels of brightness (all shades of grey), they can be seen but without any colour detail. Hence the eyes won’t discern a shape or number .
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I thought colourblind people couldn’t see the difference between certain colours not that they saw the world in black and white, they aren’t dogs. I was told that most colour blind people can’t see any difference between red and green, very few only see in monochrome.
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I think you are right Bruce. There are degrees of colour blindness but I’m fairly sure it still comes gown to the luminance values if colour is discounted altogether. I think that’s why the test works.
Edit: There are online tests for colour-blindness. Numbers in various colours set against various backgrounds. Some people say they can see some numbers but not others, depending on the colours used. This does show that complete colour blindness is probably rare. I still feel that the test works because of the luminance value factor though.
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I am severely colour blind and was told that around sixty years ago when I had a medical to get in the police. Apparently one in five men are to some degree.
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its that damn X chromosome, women have two of them so if one is faulty the other one repairs the damage or takes over or something like that. We men have the next to useless Y chromosome so if part of the X is dodgy we are buggered
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Speak for yourself Bruce…
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Its called Ishihara test - after the Japanese fellow who invented it.
We use it at work doing pre employment medicals - there is a book of pages, about a dozen in total, all like this, including one which people only get right if they are colour blind
and yes, much more common in men.
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Thanks 
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