What is it about the color yellow exactly that makes it subjectively less visible against a white background than say, blue or red?
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Our eyes just aren’t constructed to be able to see yellow. We see yellow when the parts of our eyes that can see red and green well both sort of see something a little bit and our brain determines that the color is between them.
The color called “yellow” in English is specifically the *lighter* shades of a range of hues between reds and greens. A dark red is still “red” in English color categories, a dark green is still “green”, but a dark yellow is typically “brown”.
That said, that’s not a complete explanation, because even equally dark yellows look lighter.
The answer lies in the [opponent process](https://en.wikipedia.org/wiki/Opponent_process). You have three cells in your eyes – S, M, and L cones (for *short*, *medium*, and *long* wavelengths) that are sensitive in the blue-violet, greenish, and yellow-greens respectively, but your brain actually sees color by comparing differences between them.
* Brightness is the sum of all three signals, S+M+L
* “Yellowness” is (M+L)-S, with “blueness” the opposite S-(M+L)
* “Redness” is L-M, and “greenness” is M-L
Since both M and L contribute to brightness, and since yellow stimulates S cells very little, yellow is close to white in terms of the structure of your visual system (with two positive components and one negative).
Blue, on the other hand, looks unusually dark, because M and L contribute *negatively* to blueness but *positively* to brightness. And red and green have neutral brightness, because they have one positive and one negative out of M or L and ignore S.
Yellow is much closer to white in the cielab color space.
This color space is made to be visually uniform. So the distance between 2 colors at which a given person distinguish the 2 colors is the same everywhere in the space.
So if you go from white to pure yellow and count the distinguishable shades of yellow for a given person, there are less than for any other hues.
Violet is the father away from white. So there are more shades of violet than any other colors.
The reason for that is that the S cone is overrepresented in color detection and not used at all for the feeling of brightness, while the M and L cones are mostly used for brightness and are underused for color distinction compared to the S cone.
The S cone peaks in blue, but the color for which the S cone dominates the most compared to the other cone is violet.
The M cone peaks in yellowisg green and that’s the color it dominates the most.
The L cone peaks in yellow, but it’s in red that it dominates the most compared to the other cones.
https://commons.m.wikimedia.org/wiki/File:Color_space_CIE_1976_(LUV)%2B(Lab)%2BcolorTemp.png
Put three squares—blue, red, and yellow—on a white background in a paint program. Convert the image to grayscale, and you’ll see that there is far less difference between the formerly yellow square and the white background compared to the formerly red and blue squares.
That’s because yellow has a high brightness value, far brighter than blue or red. You can see from the hex codes below that in terms of brightness, yellow is far closer to white than red or blue:
* Black: 000000
* White: FFFFFF
* Red: FF0000
* Green: 00FF00
* Blue: 0000FF
* Yellow: FFFF00
Your eyes use more than just color to see. It also relies heavily on *contrast.* Yellow on white creates poor contrast.
Cyan (00FFFF) and magenta (FF00FF) stand out against white better than yellow (FFFF00) because the last two digits in the six-digit hex code are for blue (a dark color) which yellow lacks.
This happens because of something called “contrast.” White is already a very light colour, so when you draw with yellow, which is also a light colour, it doesn’t look very different from the white background. It’s like trying to see a light yellow flower in a field of white snow – it can be a bit tricky.
On the other hand, colours like blue and red are darker than yellow. So, when you draw with a blue or red crayon on a white paper, they stand out more because they create a bigger difference or contrast between the colour and the white background. It’s like drawing with a dark blue crayon on the white paper – it’s easier to see because it looks quite different from the white.
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