Same photo. Two sets of eyes.Side-by-side simulation

Normal vision on the left, the filtered version on the right. The wall behind everything shifts too. That's not decoration, it's the same maths running on the background.The left panel is unmodified. The right applies the Machado transform for the selected type and severity. The page background is driven by the identical transform, so the entire viewport reflects the selected simulation rather than only the image pairs.

Whose eyesDeficiency type

Compare other strengthsSeverity comparison

MildLow severity ModerateModerate severity StrongHigh severity CompleteDichromacy 80%

If you took the test, this already starts where your answers put you. Move it to see how much the same picture varies across the range. The far end is the rare, total version: real, but not what most of us live with.Severity 1.0 corresponds to dichromacy (the complete absence of a functioning cone class), which is considerably rarer than anomalous trichromacy. Intermediate values are interpolated between the published matrices.

03 One picture, up close

Ripe red berries scattered through dense green leaves. — The picture as it was made, with nothing done to it. This is the one everybody else is looking at.Unmodified source image. No transform applied.

01 Foliage

The berries do not disappear. Look again: they are right there, and they are the colour of dead leaves. Nothing is missing, so nothing looks wrong. That is the part that is hard to explain, and it is why ripe and rotten is a guess.Frugivory is the standard evolutionary account of primate trichromacy. Under a red-green transform the berries retain their full luminance contrast against the foliage and remain trivially detectable; what is lost is the chromatic signal that classifies them as ripe. The failure mode is misidentification, not omission.

04 A few more pairs. Some are just paint, some are the real thing.

A dusty rose swatch beside a vivid red one, obviously two different colors. — A dusty pink next to a bright red. Red-green vision drags them most of the way together, but this is the stubborn pair on the page: some difference survives, because pink carries blue in it and blue is not what goes missing.Rose pink against saturated red. Both red-green forms compress the separation substantially without eliminating it, because the short-wavelength component of the pink is untouched by an L or M cone shift.

The same two swatches, now close enough that you would have to be told they were different. — A dusty pink next to a bright red. Red-green vision drags them most of the way together, but this is the stubborn pair on the page: some difference survives, because pink carries blue in it and blue is not what goes missing.Rose pink against saturated red. Both red-green forms compress the separation substantially without eliminating it, because the short-wavelength component of the pink is untouched by an L or M cone shift.

A very dark navy swatch beside a very dark purple one, different in hue but similar in brightness. — Navy and purple. Purple is blue with red mixed into it, so when the red stops arriving, purple just becomes navy. This is the one that ruins picking a shirt in a dim room.Deep navy against violet. Violet excitation is split between short and long wavelengths, so removing the long-wavelength contribution collapses it onto the navy, leaving almost nothing between them under either red-green form.

The same two swatches, now essentially one color shown twice. — Navy and purple. Purple is blue with red mixed into it, so when the red stops arriving, purple just becomes navy. This is the one that ruins picking a shirt in a dim room.Deep navy against violet. Violet excitation is split between short and long wavelengths, so removing the long-wavelength contribution collapses it onto the navy, leaving almost nothing between them under either red-green form.

A muted olive green swatch next to a mid brown one, clearly different. — Olive green and brown. For the most common kind of colorblindness these are not two colors that happen to look alike. They are one color with two names.Olive against mid brown. The M-cone shift that defines deuteranomaly removes very nearly all of the separation between them.

The same two swatches, now the same muddy color twice over. — Olive green and brown. For the most common kind of colorblindness these are not two colors that happen to look alike. They are one color with two names.Olive against mid brown. The M-cone shift that defines deuteranomaly removes very nearly all of the separation between them.

A clear blue-green teal swatch beside a neutral grey swatch of matching brightness. — Teal against a plain grey of the same brightness. The teal gives up almost all of its color and settles into the grey, which is why people end up asking, out loud, whether that is grey or green.Protanomaly and deuteranomaly both nearly erase this difference, since teal's hue is exactly the information a shifted L or M cone stops carrying.

The two swatches now read as the same grey, twice. — Teal against a plain grey of the same brightness. The teal gives up almost all of its color and settles into the grey, which is why people end up asking, out loud, whether that is grey or green.Protanomaly and deuteranomaly both nearly erase this difference, since teal's hue is exactly the information a shifted L or M cone stops carrying.

05 Pictures that stop working

A close-up of a red, black and white tartan weave, its checks crossing diagonally across the frame. — A red, black and white tartan flannel, photographed close enough to see the weave. For red-weak vision, red does not slide toward green here, it slides toward black, and the two dominant bands crowd together until the plaid reads as one dark check instead of two colors.Red/black/white tartan, macro detail. Protanomaly's shifted L-cone response lowers the perceived luminance of long wavelengths, darkening red toward black rather than toward green, so the weave's two dominant bands converge under the transform.

PhotoPhotographer: Andres Rivas

The same weave, the red rows now sunk almost to the same dark shade as the black ones. — A red, black and white tartan flannel, photographed close enough to see the weave. For red-weak vision, red does not slide toward green here, it slides toward black, and the two dominant bands crowd together until the plaid reads as one dark check instead of two colors.Red/black/white tartan, macro detail. Protanomaly's shifted L-cone response lowers the perceived luminance of long wavelengths, darkening red toward black rather than toward green, so the weave's two dominant bands converge under the transform.

PhotoPhotographer: Andres Rivas

A boy seen from behind in a red jersey numbered six, standing alone on a green artificial turf field with a goal in the distance. — A boy in a red team jersey, standing on green turf. Red-green colorblindness doesn't just blur two teams' kits together, it can pull a red kit toward the same shade as the grass behind it.A red kit against green artificial turf, the two dominant hue bands whose separation both deuteranomaly and protanomaly compress most.

PhotoPhotographer: Omar Ramadan

The same photo, the red shirt now sitting close enough to the green field that it barely stands out. — A boy in a red team jersey, standing on green turf. Red-green colorblindness doesn't just blur two teams' kits together, it can pull a red kit toward the same shade as the grass behind it.A red kit against green artificial turf, the two dominant hue bands whose separation both deuteranomaly and protanomaly compress most.

PhotoPhotographer: Omar Ramadan

A close-up of a red kilim rug woven with orange diamonds, dark purple crosses, and a narrow striped band of blue, green, and cream. — A kilim rug, its red field carrying a lattice of orange diamonds, indigo crosses, and a striped band of green and violet. Busy, multicolor weaves like this are where the confusion really shows.A multicolor kilim: red ground, orange and indigo lattice motifs, and a central striped band mixing green and violet, several of the hue families this page already shows collapsing on their own.

PhotoPhotographer: Engin Akyurt

The same weave, several of those colors now reading as close variants of one another instead of a rug's worth of distinct threads. — A kilim rug, its red field carrying a lattice of orange diamonds, indigo crosses, and a striped band of green and violet. Busy, multicolor weaves like this are where the confusion really shows.A multicolor kilim: red ground, orange and indigo lattice motifs, and a central striped band mixing green and violet, several of the hue families this page already shows collapsing on their own.

PhotoPhotographer: Engin Akyurt

A sage-green wall with a ragged patch of plaster missing, revealing red brick underneath, beside a stencilled house number and the dark hull of an upturned boat. — A sage-green wall where a patch of plaster has broken away to show the brick underneath. On typical vision it's an obvious repair. To red-green eyes the brick and the paint around it can end up close to the same shade, and the damage nearly disappears.Sage-green masonry paint with an exposed brick-red patch of render damage. Sage and terracotta sit close to the protan and deutan confusion line, converging toward a shared mid-tone under either transform.

PhotoPhotographer: Eric Lane Barnes

The same wall, the exposed brick now close enough in shade to the paint that the damage is easy to miss. — A sage-green wall where a patch of plaster has broken away to show the brick underneath. On typical vision it's an obvious repair. To red-green eyes the brick and the paint around it can end up close to the same shade, and the damage nearly disappears.Sage-green masonry paint with an exposed brick-red patch of render damage. Sage and terracotta sit close to the protan and deutan confusion line, converging toward a shared mid-tone under either transform.

PhotoPhotographer: Eric Lane Barnes

Try one of your ownUpload an image

Drop in a photo and the same filter runs on it. It never leaves your browser. There's nowhere for it to go, because there's no server here to send it to.Images are processed entirely client-side via CSS filters on an object URL. No upload occurs; the site is statically hosted and has no endpoint capable of receiving one.

Choose a photoSelect an image file