Color blindness: the types explained

See it for yourself

One set of colors through each kind of color vision — then the fix.

Typical color vision

A link that is only a different color can vanish here. Toggle the underline option and it survives every filter — that is the whole design lesson in one line.

How it works

Three sensors, one comparison

Your eye reads color with three kinds of cone cell, each tuned to a different band of light — long, medium, and short wavelengths, roughly red, green, and blue. No cone sees a color on its own. Every color you experience is your brain comparing the strength of those three signals, the way you can tell where a sound came from by comparing what each ear heard.

Two of the sensors are nearly twins

The long and medium cones — the red-ish and green-ish ones — respond to bands that overlap heavily, so telling red from green rests on the small difference between two very similar sensors. Lose either one and that difference is gone. With no long cone (protanopia), reds and greens merge and reds also look dark. With no medium cone (deuteranopia, the most common missing-cone type), they merge at normal brightness. The other types are rarer: tritanopia is a missing short cone, so blues suffer instead, and achromatopsia — no color signal at all — is very rare. Most often a cone is weakened rather than missing; those are the "-anomaly" forms, milder but built on the same logic.

What the demo is doing

The demo above cannot switch off a cone in your eye, so it does the next best thing: a filter that remaps every color to roughly what remains when one sensor's contribution drops out. It is an approximation, but a fair one — flip between typical vision and deuteranopia and watch the red and green swatches walk toward each other until they meet.

Where it came from

The first scientific account of color blindness was a self-portrait. In 1794 the chemist John Dalton described his own color vision — carefully, publicly, as a scientist reporting on the one instrument he could not step outside of. The description stuck so firmly to his name that in many languages the condition is still called Daltonism.

The test most people actually meet came more than a century later. In 1917, Shinobu Ishihara published his dot-plate test: circles of colored dots hiding a number, drawn so the number differs from the background only in a pair of hues that one type of color vision cannot separate. If your cones can split that pair, the number is obvious; if they cannot, the plate is noise. It is still in use today.

There is a thread worth noticing between the two: the field began with someone being honest about what he could not see. Two centuries on, honesty about what different eyes see is still where good design starts.

Who it helps — honestly

Color blindness is common — about 1 in 12 men and about 1 in 200 women have a red-green type. The gap is genetics: the genes for the red and green cones ride on the X chromosome. Men have one X, so one affected copy is enough; women have two, so a working copy on the other X usually covers for it.

Here is the honest limit: no filter, lens, or setting gives back a missing cone. Shifting colors can push a confusing pair apart so they read as different, which genuinely helps — but every shift moves other colors too, and what works for one person's eyes can make things worse for another's. Tools in this space are adjustments to try, not cures.

The fix that works for everyone lives on the design side, and it fits in one sentence: never make color the only way to tell things apart. That rule is written into the web's accessibility guidelines as WCAG 1.4.1, and the demo above shows why — underlines, patterns, and labels survive every one of the four filters, while color-only links vanish. Turn on the underline toggle and flip through the types: the link never disappears. That is exactly what Helperbird's link underlining does on every page you visit.

Try it in Helperbird

Helperbird brings these tools to any website, PDF, or Google Doc — no copying text anywhere, and nothing you read leaves your browser.

Color blindness support Filters and link underlining that keep pages usable whatever your color vision.

Step-by-step: How to adjust color saturation on any website

Questions people ask

What is the difference between protanopia and deuteranopia?

Both make red and green hard to tell apart, but for different reasons: protanopia is a missing red sensor and also makes reds look dark, while deuteranopia is a missing green sensor with normal brightness. The demo lets you compare them on the same colors.

What is tritanopia?

The rare blue type: the blue-sensitive cone is missing, so blue and green blur together and yellows can look pink. It affects far fewer people than the red-green types.

How common is color blindness?

Roughly 1 in 12 men and 1 in 200 women have some form of red-green color vision deficiency — in a class of thirty, that is usually at least one person.