Color Blindness Simulator
See an image or a color palette the way people with color blindness see it, and find colors that clash.
Loading Color Blindness Simulator… If nothing happens, please enable JavaScript.
About one man in twelve and one woman in two hundred see colour differently from everyone else. Most of them are not blind to colour at all: one of the three types of cone cells in their eyes is missing or shifted, so some colours that look clearly different to you look the same to them. Red and green are the classic pair, but brown and green, blue and purple, pink and grey, and orange and yellow-green can also merge. This simulator shows you what that looks like. Load a photo, a screenshot, a chart, a map, a game interface or a slide, and you see it next to the way it appears with each main type of colour blindness, all at once or side by side.
Examples
#d62728 + #2ca02c
#8c7917 + #988434
Red and green under deuteranopia (Brettel 1997): both turn olive brown. The classic chart problem, listed with a small OKLab distance.
#1f77b4 + #9467bd
#4e75b4 + #3b72bd
Blue and purple under protanopia: purple loses its red part, so two similar blues are left.
Frequently asked questions
Is my image uploaded anywhere?
Which type of color blindness is the most common?
What is the difference between deuteranopia and deuteranomaly?
Which model should I choose, Brettel or Machado?
How accurate is the simulation?
How do I make a chart readable for color blind people?
What does the distance number in the Colors tab mean?
Can I simulate color blindness for a whole website?
About Color Blindness Simulator
Four types are simulated. Protanopia (missing red cones) and deuteranopia (missing green cones) are the two forms of red-green colour blindness and together cover the vast majority of cases. Tritanopia (missing blue cones) is rare and confuses blue with green and yellow with pink. Achromatopsia means seeing in shades of grey only. Most people with a colour vision deficiency actually have a milder form, an anomalous trichromacy, where the cone is present but tuned to the wrong wavelength: deuteranomaly alone affects about 5% of men. The severity slider covers this: at 100% you see the full dichromacy (protanopia, deuteranopia, tritanopia), below 100% the milder protanomaly, deuteranomaly and tritanomaly.
The maths follows the published research rather than a quick filter. You can choose between two models. Brettel, Viénot and Mollon (1997) is the reference for complete colour blindness and the only common model that handles tritanopia well. Machado, Oliveira and Fernandes (2009) was built around the anomalous forms and gives a separate matrix for each severity step. Both are applied in linear light, after removing the sRGB gamma curve, which is the way they were designed to be used; many online simulators skip that step and make reds and greens look darker than they should. The image never leaves your device: it is decoded and processed in your browser, and you can download any version, or all of them in a .zip, as PNG, WebP or JPEG.
The Colors tab is for designers and anyone building charts, dashboards, maps or brand palettes. Paste a list of hex codes and you get each colour as it appears for every type, plus a list of the pairs that become hard to tell apart, measured as a perceptual distance in the OKLab colour space. That tells you exactly which series in a chart or which states on a map will be confused, before anyone has to ask. The usual fix is not to avoid colour, but never to rely on it alone: vary lightness as well as hue, add labels, icons, patterns or line styles, and check again.
The chemist who described his own colour blindness
In 1794 the English chemist John Dalton, better known for atomic theory, read a paper to the Manchester Literary and Philosophical Society describing how he and his brother saw colours differently. A pink geranium looked sky blue to him by daylight and yellowish by candlelight, and he had once bought his mother what he thought were sober grey stockings, which turned out to be bright scarlet. He guessed that the fluid inside his eyes was tinted blue and asked for his eyes to be examined after his death. They were, and the fluid was perfectly clear. The word daltonism for colour blindness still survives in French, Spanish, Portuguese and several other languages.
The question was settled in 1995, when researchers extracted DNA from Dalton's preserved eye tissue, kept at the Manchester Literary and Philosophical Society for more than 150 years. They found that he lacked the gene for the medium wavelength (green) photopigment: Dalton was a deuteranope, more than two centuries after he described the symptoms himself.
The best known test for red-green colour blindness came later, in 1917, when the Japanese ophthalmologist Shinobu Ishihara designed his plates of coloured dots for the Imperial Army. Each plate hides a number in dots whose colours differ only along the red-green axis, with lightness and size randomised so that nothing else gives the figure away. The plates are still the standard screening test more than a hundred years later.