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

Imagine looking at a traffic light and not being able to tell the difference between red and 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 less than 0.5% of women around the world live with this every day. It’s called red-green color blindness, and it’s not a disease. It’s a genetic quirk - one that’s been passed down for generations, often without anyone realizing why.

What Actually Happens in Your Eyes?

Your eyes have three types of cone cells that detect color: one for red, one for green, and one for blue. These cones contain light-sensitive proteins called photopsins. In people with red-green color blindness, the red or green photopsins don’t work right. Sometimes they’re missing. Sometimes they’re swapped. Sometimes they’re just slightly off. The problem lies in two genes: OPN1LW for red cones and OPN1MW for green cones. These genes sit on the X chromosome - the same one that determines biological sex. That’s why this condition hits men far more often than women. Men have one X and one Y chromosome. If the X they inherit from their mom carries a faulty red or green gene, they’ll have color blindness. Women have two X chromosomes. They’d need both to carry the mutation to be affected. That’s statistically unlikely. So while 1 in 12 men have it, only about 1 in 200 women do.

The Two Main Types: Protanopia and Deuteranopia

There are two major forms of red-green color blindness, and they’re named after which cone is affected.

• Protanopia means the red cones are missing or non-functional. Reds look dark, almost black. Some greens and yellows get mixed up too.
• Deuteranopia means the green cones are gone. This is the most common type - affecting about 5% of men. Reds and greens look muddy, like different shades of beige.

Then there are the milder versions: Protanomaly and Deuteranomaly. These aren’t full losses - just faulty pigments. People with deuteranomaly can still see most colors, but they struggle with subtle differences, like telling apart a bright red apple from a ripe tomato.

Why Is This Inherited So Unevenly?

It all comes down to biology. Women have two X chromosomes. Even if one carries the color-blind gene, the other often compensates. Men don’t have that backup. If their single X has the mutation, they’re affected.

This isn’t just theory. Genetic studies from the National Eye Institute show that the red and green genes sit next to each other in a row on the X chromosome. During sperm production, these genes can accidentally swap places or delete parts of themselves. That’s why you’ll sometimes see a man with a hybrid gene - part red, part green - that doesn’t work properly.

And here’s the kicker: if a man has red-green color blindness, he won’t pass it to his sons. Why? Because he gives his sons his Y chromosome, not his X. But he will pass the faulty gene to all his daughters. They’ll become carriers - and if they have sons, those sons have a 50% chance of being color blind.

How Is It Diagnosed?

The most common test is the Ishihara Color Test. It’s those plates with colored dots that form numbers. People with normal vision see a 5. Someone with deuteranopia might see a 2. Or nothing at all.

But that’s just the start. Eye doctors now use more advanced tools like the Farnsworth-Munsell 100 Hue Test, which asks you to arrange colored caps in order. It’s not just about seeing red or green - it’s about how finely you can tell them apart.

Most people aren’t diagnosed until school, when color-coded lessons trip them up. A child might pick the wrong crayon, or fail to spot the red circle in a group of green ones. Teachers often notice first.

It’s Not Just About Traffic Lights

People assume color blindness is about missing red or green. But it’s more than that. It’s about missing contrast between colors that look similar.

• Electrical wires: red and green can look identical. Many electricians use tape labels or numbered tags to avoid mistakes.
• Food: undercooked chicken and rare steak can look the same. A person with color blindness might rely on texture or a meat thermometer.
• Maps and charts: green lines on a map might blend into brown hills. Graphs with red bars next to green ones can be unreadable.
• Weather apps: red for heat, blue for cold - if you can’t tell the difference, you’re guessing.

A 2022 survey of over 1,200 people with red-green color blindness found that 78% struggled with color-coded school materials. 65% had trouble with traffic lights in poor weather. And 42% said apps and websites were hard to use because colors weren’t paired with symbols or labels.

Can You Fix It?

There’s no cure. But there are tools.

EnChroma glasses are the most well-known. They cost between $329 and $499 and use special filters to block overlapping wavelengths of light. This helps separate red and green signals. Studies show about 80% of users report improved color distinction - but it’s not magic. It doesn’t restore normal vision. It just makes some colors pop more clearly.

Then there are digital tools. Color Oracle is a free app that lets designers see how their work looks to someone with color blindness. Sim Daltonism does the same on phones. The Colorblindifier plugin for Photoshop has been downloaded over 45,000 times.

Even big tech companies are stepping in. Apple’s iOS has had color filters since 2014. Microsoft added them to Windows in 2015. These let users shift colors to make them more distinguishable. Around 0.8% of iPhone users turn them on - which might sound small, but that’s hundreds of thousands of people.

What About Careers?

Some jobs still screen for color vision - and that’s controversial.

Pilots, electricians, firefighters, and military roles often require passing color tests. A Reddit user named “ProtanopePilot” shared how he was turned down for a commercial pilot license despite having perfect 20/20 vision. He could see the lights - just not the colors. He passed every other test. But the rules didn’t care.

In the UK, the Equality Act 2010 says color blindness can be a disability if it limits daily activities. Between 2015 and 2022, over 1,200 workplace discrimination claims were filed related to color vision. Some employers now use alternatives: labels on wires, audio cues, or digital assistants.

What’s Next?

Science is moving fast. In 2022, researchers at the University of Washington used gene therapy to restore full color vision in adult squirrel monkeys. They injected a normal copy of the missing gene into the retina. The monkeys could see red and green for over two years. It’s not ready for humans - but it’s proof that it’s possible.

The National Eye Institute is investing millions into restoring color vision. Meanwhile, companies like EnChroma are rolling out new lens tech that improves color discrimination by 30% over older models.

And globally, the ColorADD system - a set of simple symbols that represent colors - is now used in public transport systems across 17 countries. A subway map doesn’t need red and green lines anymore. It can use a star, a circle, and a square.

Living With It

Most people with red-green color blindness don’t see it as a tragedy. A survey by Colour Blind Awareness found that 92% consider it a minor inconvenience. One graphic designer on Reddit said, “I used to fight it. Now I design with contrast in mind. It made me better at my job.”

You don’t need to fix it. You need to adapt. Use labels. Use patterns. Use apps. Ask for help. And if you’re designing something - make sure it works for everyone, not just the 99% who see colors the same way.

It’s Not Blindness. It’s Different Vision.

The word “color blind” is misleading. People with this condition aren’t blind. They see color - just differently. Their world isn’t grayscale. It’s a palette with fewer distinctions. And many of them navigate it better than you’d think.

The real problem isn’t their eyes. It’s a world built for one kind of vision - and not enough thought given to the others.