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

Most people think color blindness means seeing the world in black and white. But for the vast majority of people with this condition, it’s not about missing color entirely-it’s about mixing up reds and greens. Think of a red apple next to a green leaf. To someone with normal vision, the difference is obvious. To someone with red-green color blindness, they might look almost identical. This isn’t a flaw in their eyesight-it’s a genetic quirk, passed down through families in a way that explains why it’s far more common in men than women.

What Exactly Is Red-Green Color Blindness?

Red-green color blindness isn’t one single condition. It’s a group of related vision differences caused by problems with the light-sensitive pigments in your eyes’ cone cells. These cones come in three types: one for red light, one for green, and one for blue. When the red or green cones don’t work right, your brain gets mixed signals. That’s when reds look dull, greens turn brownish, and oranges and yellows start to blend together.

The two most common forms are deuteranomaly and protanopia. Deuteranomaly means your green cones are faulty but still somewhat functional. It’s the most common type, affecting about 5% of men. Protanopia means you’re missing your red cones entirely. That’s rarer, but it makes reds look darker and more like black or gray. There’s also protanomaly (weak red cones) and deuteranopia (no green cones), but these are less frequent.

What’s surprising is that most people with this condition don’t even realize they’re different until they’re tested. A child might pick the wrong crayon in art class. An adult might struggle to tell if a tomato is ripe or if a traffic light is red or green. Many learn to adapt-using brightness, position, or context instead of color alone.

Why Is It More Common in Men?

The reason men are affected far more often than women comes down to biology-and chromosomes. The genes that make the red and green pigments are located on the X chromosome. Men have one X and one Y chromosome. Women have two X chromosomes.

If a man inherits an X chromosome with a faulty color vision gene, he has no backup. His Y chromosome doesn’t carry a replacement. So he’ll have color blindness. But a woman needs two faulty copies-one on each X chromosome-to be affected. That’s rare. Statistically, about 8% of men have some form of red-green color blindness. Only about 0.5% of women do.

This pattern is called X-linked recessive inheritance. It’s the same reason conditions like hemophilia are more common in men. A mother can carry the gene without being affected herself. She can pass it to her sons. If a son inherits the faulty gene, he’ll have the condition. Daughters can inherit it too, but they’ll usually be carriers unless both parents pass on the gene.

How Is It Passed Down? A Family Tree Example

Let’s say a man has red-green color blindness. He passes his X chromosome with the faulty gene to all his daughters-but none of his sons (because sons get his Y chromosome). So all his daughters become carriers. If one of those daughters has a son, there’s a 50% chance he’ll inherit the faulty gene and be color blind.

Now imagine a woman who is a carrier. She has one normal X and one faulty X. Each son has a 50% chance of being color blind. Each daughter has a 50% chance of being a carrier. Only if she has a son who inherits the faulty X and a daughter who inherits the faulty X from both her and her color-blind father will that daughter be affected.

This is why you’ll often see color blindness skip generations. A grandfather might be affected. His daughter isn’t. But her son is. The trait didn’t disappear-it was hidden in the mother.

How Do Scientists Know It’s Genetic?

Back in 1798, John Dalton-yes, the same Dalton who developed atomic theory-wrote about his own trouble seeing red and green. He was one of the first to describe the condition scientifically. Today, we know his symptoms were caused by a mutation in the OPN1LW gene, which controls red pigment production.

Modern genetics has mapped the exact location of these genes: Xq28, on the long arm of the X chromosome. There’s one gene for red (OPN1LW), but multiple copies for green (OPN1MW). These genes sit next to each other in a row. During reproduction, they can accidentally swap parts. That’s how hybrid genes form-genes that are part red, part green-and why some people see colors differently than others.

Studies from the National Eye Institute and the University of Arizona show that the most common cause isn’t a single point mutation. It’s a recombination error-a glitch during sperm or egg formation-that deletes or fuses these pigment genes. That’s why the condition runs in families and doesn’t pop up randomly.

How Is It Tested?

The most famous test is the Ishihara test. It uses plates filled with colored dots that form numbers. People with normal vision see one number. People with red-green color blindness see a different number-or nothing at all. It’s simple, fast, and still used in schools, eye clinics, and even pilot exams.

But it’s not perfect. Some people memorize the patterns. Others with mild forms pass the test but still struggle in real life. That’s why some doctors now use more advanced tools like the Farnsworth-Munsell 100 Hue Test, which asks you to arrange colored caps in order. It’s more precise.

There are also digital tools like Color Oracle and Sim Daltonism. These apps simulate how the world looks to someone with color blindness. Designers use them to make websites, apps, and charts easier to read for everyone.

What Does It Mean in Daily Life?

For most people, color blindness is a minor inconvenience. But in some situations, it can be a real problem.

• Electrical wiring: Red and green wires can be hard to tell apart. Many electricians label wires with numbers or use texture.
• Food: Ripe vs. unripe fruit, cooked vs. raw meat-these distinctions rely on color. People learn to check texture or use thermometers instead.
• Maps and charts: Color-coded graphs can be confusing. Good design uses patterns, labels, or brightness differences too.
• Driving: Traffic lights are usually arranged in the same order (red on top, green on bottom). But in fog or glare, that’s not enough. Some drivers use special filters or rely on the position of the light.
• Clothing: Matching socks or shirts can be a challenge. Many people stick to neutral tones or use apps that identify colors via smartphone cameras.

One Reddit user, a commercial pilot, wrote: “I had 20/20 vision. But I failed the color test. I couldn’t become a pilot-even though I could see the lights fine.” That’s the reality. Some careers still require perfect color vision, even if the person can function well in daily life.

Can It Be Fixed?

No cure exists. You can’t change your genes. But there are tools that help.

EnChroma glasses are the most well-known. They cost between $330 and $500 and use special filters to block certain wavelengths of light. This helps the brain separate red and green signals better. About 80% of users report improved color perception. But they don’t restore normal vision. And they don’t work for everyone-especially those with complete loss of a cone type.

There are also apps and browser extensions that adjust screen colors. Microsoft and Apple both offer built-in color filters in their operating systems. These let you shift colors to make reds and greens stand out more.

And then there’s the future. In 2022, scientists successfully gave color vision to adult squirrel monkeys using gene therapy. They injected a normal human red pigment gene into the monkeys’ eyes. Within weeks, the monkeys could tell red from green for the first time. The effect lasted over two years. It’s early, but it proves the brain can learn to use new color signals-even as an adult.

That doesn’t mean a cure for humans is around the corner. But it does mean that someday, gene therapy might help people with red-green color blindness see the full spectrum.

What’s Being Done to Help?

More than just tech, there’s growing awareness. The Web Content Accessibility Guidelines (WCAG 2.1) require websites to use color in ways that don’t rely on it alone. Buttons must have labels. Charts must have patterns. That’s not just good design-it’s the law in many places, including the European Union.

Companies like Adobe offer free plugins like Colorblindifier, which lets designers see how their work looks to someone with color blindness. Over 45,000 people have downloaded it since 2015.

Even public transit systems are adapting. Portugal’s ColorADD system uses simple shapes-like triangles or circles-to label colors on maps and signs. It’s now used in 17 countries.

And legally, in places like the UK, color blindness is recognized as a disability under the Equality Act. Employers must make reasonable adjustments. If someone can’t read a color-coded chart, they’re entitled to a version with labels.

Is It Really a Disability?

Most people with red-green color blindness don’t see it that way. A 2022 survey by Colour Blind Awareness found that 92% consider it a minor inconvenience. Only 37% said they felt embarrassed by color-matching mistakes. Many say it’s just part of who they are.

One graphic designer wrote: “I used to think I was bad at color. Then I learned to use contrast and texture. Now I design better than most people who see color the ‘normal’ way.”

It’s not about seeing less. It’s about seeing differently. And that difference, while genetic, doesn’t have to hold you back.