Color Blindness: Understanding Red-Green Defects and How They're Inherited

Most people think of color blindness as seeing the world in black and white. But for the vast majority of those affected, it’s not about missing color entirely-it’s about struggling to tell red and green apart. This isn’t a rare oddity. About 8% of males and 0.5% of females worldwide live with red-green color blindness, making it the most common type of color vision deficiency. And it’s not something you develop later in life-it’s written into your genes from birth.

How Red-Green Color Blindness Actually Works

Your eyes have three types of cone cells that detect color: one for red, one for green, and one for blue. The red and green cones are controlled by genes on your X chromosome. These genes make proteins called photopsins that react to light. When they work properly, you see a full spectrum. When they’re faulty or missing, your brain gets confused between reds, greens, browns, and oranges.

There are two main forms of red-green color blindness: protanopia and deuteranopia. Protanopes lack the red cone pigment entirely. Deuteranopes lack the green one. A less severe version-protanomaly and deuteranomaly-means the pigments are there but don’t work right. Deuteranomaly is the most common, affecting about 5% of men. People with this condition don’t see the world in grayscale. They just mix up colors that look very similar to them, like maroon and green, or peach and pink.

It’s not a vision problem like nearsightedness. Your sharpness, depth perception, and night vision are usually perfect. You just see colors differently. That’s why many people don’t realize they’re color blind until they’re tested-or until they make a mistake, like picking the wrong wire in an electrical panel or misreading a traffic light in fog.

Why Men Are Much More Likely to Be Affected

The reason men are nearly 16 times more likely to have red-green color blindness than women comes down to biology. The genes for red and green vision are on the X chromosome. Men have one X and one Y chromosome. Women have two X chromosomes.

If a man inherits a faulty gene on his single X chromosome, he has no backup. He’ll be color blind. But a woman needs to inherit two faulty copies-one from each parent-to be affected. If she has only one bad copy, she’s a carrier. She usually sees colors normally but can pass the gene to her children.

This is why the math works out the way it does. If 8% of men are affected, that means about 8% of X chromosomes in the population carry the mutation. For a woman to be affected, both of her X chromosomes need the mutation. That’s 8% of 8%, or about 0.64%. In reality, it’s closer to 0.5% because of how X chromosomes randomly switch off in female cells-a process called X-inactivation. That’s why you rarely see women with full color blindness, even when their fathers are affected.

How It’s Passed Down in Families

Here’s how it actually plays out in families:

• A color-blind father will pass his faulty X chromosome to all his daughters-but none of his sons. His sons get his Y chromosome, not the X.
• A carrier mother (with one faulty gene) has a 50% chance of passing it to each child. If she passes it to a son, he’ll be color blind. If she passes it to a daughter, the daughter will be a carrier.
• If a color-blind man has a daughter with a woman who isn’t a carrier, all his daughters will be carriers, and none of his sons will be affected.
• If a carrier woman has a son, there’s a 50% chance he’ll be color blind. If she has a daughter, there’s a 50% chance she’ll be a carrier.

That’s why you’ll often see color blindness skip generations. A grandfather passes it to his daughter (who doesn’t show symptoms), and she passes it to her son. The pattern looks random, but it’s predictable once you understand the X-linked inheritance.

What It Feels Like in Real Life

For many, it’s not a disability-it’s just how they see the world. But there are real challenges.

One man, a commercial pilot applicant, was disqualified because he couldn’t pass the standard color test-even though his vision was 20/20. Another, an electrician, relies on numbered wire labels instead of color codes. A graphic designer learned to use brightness and patterns instead of color alone, which actually improved her designs.

Surveys show that 78% of people with red-green color blindness struggle with color-coded school materials. 65% have trouble with traffic lights in poor weather. 42% say apps and websites are hard to use when information is only shown in color.

And then there’s the social stuff. A 2022 survey found that 37% of people with color blindness have been embarrassed by mismatched clothes. Imagine wearing a red shirt with brown pants and thinking you look fine-only to be told it looks like a mistake. It’s not about fashion. It’s about not knowing you’re seeing something differently.

Testing and Diagnosis

The most common test is the Ishihara test. It’s made of colored dots that form numbers. People with normal color vision see one number. Those with red-green deficiency see a different number-or nothing at all.

But the Ishihara test isn’t perfect. It can miss mild cases. More advanced tests like the Farnsworth-Munsell 100 Hue Test or the anomaloscope (which lets you match colors by adjusting brightness) give a clearer picture. These are used in medical settings and for jobs where color accuracy matters-like aviation, electrical work, or graphic design.

Most people aren’t tested unless they’re applying for a job or a school program that requires it. Many live their whole lives without knowing they’re affected.

Tools and Adaptations That Help

There’s no cure-but there are tools that make life easier.

EnChroma glasses, introduced in 2012, cost between $329 and $499. They don’t restore normal color vision. But for about 80% of people with red-green deficiency, they make colors pop in a way that feels more distinct. A 2023 update to their lenses improved results for deuteranomaly by 30%.

For digital accessibility, tools like Color Oracle (free) and Sim Daltonism (paid) let designers see how their apps look to color-blind users. Adobe Photoshop has a free plugin called Colorblindifier that’s been downloaded over 45,000 times.

Big tech companies have built in color filters. Apple’s iOS has had them since 2014. Microsoft’s Windows 10 has them too. Over 2.3 million people have used Microsoft’s filter. That’s not a small number-it’s millions of people adapting their tech to fit how they see.

And then there’s ColorADD, a system developed in Portugal that uses simple shapes to represent colors. A triangle is red. A circle is green. A square is blue. It’s now used in public transit systems in 17 countries, on clothing tags, and in school materials. It’s not about fixing vision-it’s about designing around it.

What the Future Holds

Science is making progress. In 2022, researchers gave gene therapy to adult squirrel monkeys with red-green color blindness-and restored their full color vision for over two years. That’s huge. It proves the brain can learn to use new color signals, even as an adult.

The National Eye Institute is funding research to bring this to humans. It’s not going to happen tomorrow. But the goal is clear: one day, a simple injection could restore normal color vision for those born with the deficiency.

In the meantime, accessibility is improving. The Web Content Accessibility Guidelines (WCAG 2.1) now require websites to use patterns, labels, and contrast-not just color-to convey information. The European Union’s Accessibility Act makes this mandatory for public services. And in the UK, the Equality Act 2010 recognizes color blindness as a disability that requires workplace accommodations.

So while you can’t change your genes, you can change how the world adapts to you. And that’s where real progress is happening.

Common Myths About Color Blindness

• Myth: Color blind people see only in black and white. Truth: Only about 1 in 30,000 people have true monochromatic vision. Most see color-they just don’t distinguish red and green well.
• Myth: Color blindness gets worse with age. Truth: It’s genetic and stable. If you’re born with it, you’ll have it your whole life. It doesn’t get worse.
• Myth: Only men can be color blind. Truth: Women can be affected, but it’s rare. They need two faulty genes.
• Myth: Glasses can cure it. Truth: They help some people see better, but they don’t fix the biology. Think of them like hearing aids for color.

What You Can Do

If you think you or someone you know might be color blind:

• Take a free online test like the Ishihara or Color Blind Check (many are available). They’re not medical-grade, but they can point you in the right direction.
• If you’re a parent, ask your child’s doctor to screen for it during routine eye checks. It’s not always part of standard exams.
• If you’re a designer, teacher, or developer, use accessibility tools. Add patterns to charts. Use labels. Don’t rely on color alone.
• If you’re affected, know that you’re not broken. You’re just wired differently. Millions of people live full, successful lives with this condition.

Color blindness isn’t a tragedy. It’s a variation. And with better awareness, better tools, and better design, the world is finally catching up.