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Something got mangled between there and here. Links do that. Nothing's broken on your end. You can still take the test yourself, or go poke at the simulator.The URL did not resolve to a known deficiency type. This is typically caused by truncation in transit. The screening test and simulator remain available.
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A shared view
This is how Zack sees the world.This simulates Zack's color vision.
Before anything else: it's not black and white.Preliminary: this is not achromatopsia
The colors are all still there. What's missing is the gap between some of them. Press the switch and watch it happen to this page, wall and all.The common assumption is a total loss of color perception. In fact all three cone classes remain functional; one is shifted, which collapses the perceptual distance between specific hue pairs. The comparisons below apply that transform to familiar images.
Everything on this page is about to change, including the wall behind it. Nothing here is a mock-up of the effect, it is the effect.The transform is applied to the entire document, background included, using the same matrices throughout rather than an approximation of the result.
That's it. That's the whole difference, and it doesn't switch off.The rendered state above is the simulated percept. Toggle it back to compare the two directly.
Colorblind yourself? Then this switch won't show you much, because your eyes already do what it does. This page is for the people you send it to.Viewers with a matching deficiency will perceive minimal change: the simulation reproduces a transform their own vision already applies. This page is addressed to typical-vision recipients.
Things that stop workingRepresentative failure cases
Ask for the green one and hope whoever hands it over can see it.Retail yarn wall: low-chroma pastel columns compress early, and the olive edge stock loses its hue identity under either red-green form.
PhotoPhotographer: ROMAN ODINTSOV
Red flowers on green leaves. This is the one everyone with the condition names first.Saturated red blooms against foliage green: the canonical red-green confusion surface, near-complete convergence at severity 0.8.
PhotoPhotographer: Egor Komarov
A paint table. Some of these cups are the same color until somebody labels them.Mixed pigment cups across the gamut: red-green members converge while the blue and yellow cups remain separated.
PhotoPhotographer: K
In practice
Same family as the common red-green kind, but reds take the hit here. A red car parked in shade can read as almost black to them, and red text on a dark background can disappear entirely. That's the part to watch for as the page shifts.Protanomaly: reduced L-cone sensitivity dims long-wavelength light in addition to compressing red-green discrimination, a luminance effect the more common deuteranomaly does not share. Prevalence is roughly 1% of men.
In practice
Their green sensitivity has drifted toward red, so the two crowd each other. A traffic light green can look almost white to them. Olive and brown can be the exact same color, not just similar. The wall behind this page is running through that same shift right now, so you're looking at it too.Deuteranomaly: a shifted M-cone peak compresses the perceptual distance between green and red. It is the most common deficiency, affecting roughly 5% of men. Discrimination is reduced; overall color perception is preserved.
In practice
This one is rare, and it doesn't split along red and green at all. Blue and green blur together for them, and yellow can wash out toward pink or grey.Tritanomaly: reduced S-cone sensitivity compresses blue-yellow discrimination. Unlike the protan and deutan forms it is not X-linked, and it occurs at similar rates in both sexes.
In practice
This is the rare condition people assume everyone with colorblindness has: color barely registers at all, and the world reads mostly as light and dark.Achromatopsia: near-total absence of functioning cone cells, leaving vision reliant on rods alone. Prevalence is around 1 in 30,000, far rarer than any form of anomalous trichromacy.
What this is showing youScope of the simulation
This shows you which colours stop being tellable apart. It is not a photograph of what is in somebody else's head, and nothing can be. Ask a colorblind person to look at the filtered version and they will usually say the red still looks red, because their eyes do the same thing to both halves, and red is the word they have always used for it.The transform demonstrates loss of chromatic discrimination, not subjective appearance. It identifies which stimulus pairs become effectively indistinguishable for the modelled observer; it makes no claim about the observer's experience, which is not externally accessible. An anomalous trichromat viewing this page applies the same transform again to both panels and will typically report little difference between them.
The exchange that made this worth sayingDiscussion of scope and the naming effect
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