Color Blindness: Understanding Red-Green Defects and How They’re Passed Down

Imagine looking at a traffic light and not being able to tell red from green. Not because you’re squinting or it’s foggy - but because your eyes just don’t see those colors the way most people do. This isn’t rare. About 8% of men and 0.5% of women live with this every day. It’s called red-green color blindness, and it’s not a disease. It’s a genetic trait, passed down like eye color or height - but with real, everyday consequences.

What Actually Happens in the Eye?

Your retina has three types of cone cells, each sensitive to a different part of the color spectrum: red, green, and blue. These cones contain proteins called photopsins that catch light and send signals to your brain. In people with red-green color blindness, one or both of the red or green photopsins don’t work right. That doesn’t mean they see in black and white. They see colors - just not the same ones you do.

There are two main types of red-green deficiency:

• Protanopia: No working red photopsin. Reds look dark, almost black. Greens and yellows can blend together.
• Deuteranopia: No working green photopsin. Reds and greens look muddy. This is the most common form.

Then there are the milder versions - protanomaly and deuteranomaly - where the photopsins are there, but they’re faulty. Deuteranomaly affects about 5% of men. Most people with this don’t even know they have it until they take a test or someone points out they’re mixing up socks.

Why Is It So Much More Common in Men?

The genes for red and green photopsins are on the X chromosome. Men have one X and one Y chromosome. Women have two X chromosomes.

That means:

• A man only needs one copy of the faulty gene - from his mom - to be color blind.
• A woman needs two copies - one from each parent - to be affected.

If a woman carries one faulty gene, she’s a carrier. She usually sees colors normally, but she can pass the gene to her kids. That’s why you see this pattern: a color-blind father passes the gene to his daughters (who become carriers), and those daughters can then pass it to their sons.

This is called X-linked recessive inheritance. It’s the same reason hemophilia and Duchenne muscular dystrophy show up more often in boys. The math is simple: if 8% of men have it, then about 0.64% of women should - and that’s close to what’s observed. The rest are carriers.

How Do You Know If You Have It?

The most famous test is the Ishihara test - those plates with colored dots forming numbers. If you can’t see the number, or see a different one, it’s a sign. But it’s not perfect. Some people pass the test but still struggle in real life.

Many people only find out when:

• They get rejected for a job that requires color discrimination - like piloting, electrician work, or graphic design.
• They’re told they’re wearing mismatched clothes.
• They’re in school and can’t tell red from green on a graph.

A simple online test can give you a clue, but a professional eye exam with a color vision test like the Farnsworth-Munsell 100 Hue Test gives the full picture.

What Does It Actually Feel Like?

People with red-green color blindness don’t see the world in grayscale. They see colors - just with less contrast between reds, greens, browns, and oranges. A ripe tomato might look like a dull brown. A green apple might look yellow. A red fire truck might look like a dark orange.

One user on Reddit, who has deuteranomaly, said: “I once tried to pick out a green shirt to match my jeans. I wore it for a week before someone asked if I was going to a Halloween party.”

For engineers, electricians, or pilots, this isn’t just awkward - it’s risky. Mixing up red and green wires can cause dangerous mistakes. That’s why many professions require color vision screening.

But here’s the surprising part: most people adapt. They learn to use context. They rely on brightness, position, or labels. One graphic designer said: “I stopped using color alone to show data. I started adding patterns. Turns out, my charts are clearer for everyone.”

Can It Be Fixed?

There’s no cure. Not yet. But there are tools.

EnChroma glasses - those expensive red-tinted lenses - don’t restore normal color vision. But for about 80% of people with red-green deficiency, they make colors feel more vivid. They help you notice the difference between a red and green stoplight. They don’t turn you into someone with full color vision - but they make the world feel less gray.

Digital tools help too. Apps like Color Oracle and Sim Daltonism let designers see how their work looks to someone with color blindness. Apple and Windows both have built-in color filters. You can turn your screen to grayscale or invert colors to make contrasts pop.

The ColorADD system - using simple symbols like triangles and circles to represent colors - is now used on public transit maps in 17 countries. It’s not about fixing vision. It’s about designing for everyone.

What About the Future?

In 2022, scientists at the University of Washington gave gene therapy to squirrel monkeys with red-green color blindness. Within weeks, they started seeing red and green like normal monkeys. The effect lasted over two years.

That’s huge. It proves the brain can learn to use new color signals - even as an adult. If it works in monkeys, could it work in humans? The National Eye Institute is investing millions to find out.

But for now, the best tools are the ones we already have: awareness, adaptation, and design that doesn’t rely on color alone.

How to Live With It - And Help Others

If you have red-green color blindness:

• Label wires, cables, and clothing.
• Use apps that simulate your vision to test your designs.
• Don’t be afraid to ask for help. Most people don’t realize how hard this is.

If you’re a teacher, designer, or employer:

• Don’t use color alone to convey meaning. Add shapes, patterns, or labels.
• Use high contrast. A bright yellow on dark blue is easier to see than red on green.
• Offer alternatives. A color-coded chart should also have numbers or icons.

The World Wide Web Consortium’s WCAG 2.1 guidelines already require this for websites. But it’s not just about compliance - it’s about inclusion.

It’s Not a Disability. It’s a Difference.

A 2022 survey of over 800 people with red-green color blindness found that 92% didn’t see it as a major problem. Most said it was just a quirk - like being left-handed or having a bad sense of direction.

But that doesn’t mean it doesn’t matter. It means we need to stop treating it like a flaw to be fixed, and start designing a world that works for everyone - whether they see red and green the same way you do, or not.

What’s Next?

If you’ve never thought about color vision before, you might now see the world differently. That’s the point. Color blindness isn’t just about one person’s eyes - it’s about how we design systems, websites, signs, and tools. The more we understand it, the better we can build a world that doesn’t leave anyone behind.

Start by checking your own designs. Is color the only way information is shown? Can someone with red-green deficiency understand it? If not, add a label, a pattern, or a shape. That’s the real innovation - not in lenses or genes, but in how we think.