How to Simulate Red Green Color Blindness Without Getting It Wrong

Ever wonder why that "urgent" red button on your website doesn't get clicked, or why your friend keeps calling your brown shoes olive green? It’s probably not just a matter of taste. They might be among the 300 million people worldwide living with Color Vision Deficiency (CVD). If you’ve ever tried to simulate red green color blindness, you probably opened a filter on your phone and thought, "Oh, okay, it just looks a bit muddy."

It's deeper than that. Much deeper.

Designing for the web or physical products without checking your color contrast is basically like building a house without a front door for 8% of men and 0.5% of women. Those are the actual stats from the National Eye Institute. We aren't just talking about a minor "oops" moment. We’re talking about people missing exit signs, failing to read data charts, or accidentally eating undercooked meat because they couldn't see the pinkness in the center.

The Science of Why Simulation Matters

Red-green color blindness isn't just one thing. It's an umbrella. You have protanopia, where the "L-cones" (long-wavelength) are missing, making reds look dark and muddy. Then there's deuteranopia, the most common version, where the "M-cones" (medium-wavelength) are gone. To these folks, greens and reds both look like a yellowish-brown.

Then there are the "anomalies." Protanomaly and deuteranomaly. These aren't "blindnesses" in the sense that the color is gone; the cones are just shifted. It’s like a radio station that’s slightly out of tune. You hear the music, but there’s a lot of static. When you simulate red green color blindness, most basic tools just flatten the colors. Real simulation needs to account for this "shifting" of the spectrum.

Why does this happen?

It’s genetic. Mostly X-linked. That’s why your uncle has it but your aunt probably doesn't. Dr. Jay Neitz, a renowned color vision researcher at the University of Washington, has spent decades studying how we can actually "cure" this with gene therapy in monkeys, but for now, the rest of us just have to deal with the world as it is. Or, we have to design better.

If you’re a developer, you might think you’ve got it covered because you used a high-contrast theme. You're wrong. Contrast is only part of the battle. If two colors have the same luminance—the same "brightness" to the eye—but different hues, a person with deuteranopia won't be able to tell them apart. They’ll just see one big blob of tan.

Tools to Actually Simulate Red Green Color Blindness

Stop guessing. Seriously. There are specific, mathematically accurate ways to see what others see.

The LMS Color Space model is the gold standard here. It models how the Long, Medium, and Short wavelength cones in the human eye react to light. When you use a high-quality simulator, it’s not just putting a "sepia" filter on your screen. It’s literally recalculating the RGB values of every pixel based on the missing sensitivity of those cones.

Browser Extensions and Software

• Color Oracle: This is the industry favorite. It’s a color blindness simulator for Windows, Mac, and Linux. What makes it great? It applies a full-screen filter. You don't have to upload a file. You just click a button, and your entire monitor—coding environment, Slack, YouTube—shifts into a protan or deutan view.
• Spectrum (Chrome Extension): If you’re strictly doing web dev, this is the one. It lets you test websites in real-time. You can see how that "Green for Go / Red for Stop" UI fails immediately.
• Adobe Illustrator & Photoshop: Did you know this is built-in? Go to View > Proof Setup > Color Blindness. Adobe uses the Brettel algorithm, which is remarkably accurate for static images.

The "Green Light" Fallacy

Think about traffic lights. Have you ever noticed that the "green" light in many modern cities looks almost white or bluish? That’s not an accident. It’s an intentional move to help people who simulate red green color blindness in their daily lives. By making the green "cool-toned" and the red "warm-toned," engineers create a secondary cue: temperature.

If the green were a "true" grassy green, it would look identical to the red to a protanope. They’d have to rely entirely on the position of the light. Top is stop, bottom is go. But what happens at night? Or in a heavy fog where you can only see one glowing orb? That's when color-coding becomes a life-or-death situation.

Real World Failures

1. The "Red" Error Message: A classic. A form field turns red when you miss a character. No icon, no text, just a red border. To a color-blind user, that border looks exactly like the grey one next to it. They’re stuck.
2. Game Design: Think of "team" colors. Red vs. Green is the classic rivalry. It’s also the worst possible choice for accessibility. Many games like Call of Duty or Overwatch now include "Colorblind Modes" that swap these to Blue vs. Orange.
3. Weather Maps: This is the worst. Look at a radar map during a storm. The transition from "heavy rain" (green) to "hail" (red) is invisible to millions. They might think they're in a light shower when a tornado is actually bearing down on them.

Designing for Everyone (The Right Way)

Don't just use a filter and call it a day. You need a strategy. The best way to design is to assume color doesn't exist at all. Start in grayscale. If your design works in black and white, it will work for everyone.

Add symbols. If a button is "Cancel," don't just make it red. Add an 'X'. If a button is "Success," add a checkmark. This is called "multi-channel signaling." You're giving the brain two different ways to process the same information.

Check your Contrast Ratios. The Web Content Accessibility Guidelines (WCAG) 2.1 suggest a contrast ratio of at least 4.5:1 for normal text. This isn't just a suggestion; in many jurisdictions, it's a legal requirement for government and public-facing sites. Use tools like WebAIM’s Contrast Checker to verify your colors.

Common Misconceptions

People think color blindness means you see in black and white. That’s achromatopsia, and it’s incredibly rare—about 1 in 30,000 people. Most people with CVD see a world full of color; it’s just a different palette. It’s more like a limited box of crayons. Instead of 64 colors, they’re working with 12.

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Another myth? That "color-correcting glasses" like EnChroma "cure" it. They don't. Those glasses work by filtering out the overlapping wavelengths between red and green. They increase the contrast between the colors, making them easier to distinguish, but they don't give you "new" cones. They're a tool, not a miracle.

Actionable Steps for Creators

If you’re serious about making your content accessible, you need to integrate simulation into your workflow. It shouldn't be an afterthought.

Run a "Squint Test." Seriously. Close your eyes halfway until everything blurs. If you can’t tell which button is which, your color contrast is too low.

Use Patterns. In data visualization, don't just use colored lines for a graph. Use a solid line for "Sales," a dashed line for "Expenses," and a dotted line for "Profit."

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Color Blindness Simulators for Mobile. Download an app called "CVSimulator" on your iPhone or Android. It uses your camera to show you the world through different CVD lenses in real-time. Walk around your office. Look at your signage. You’ll be shocked at how much information is "hidden" in plain sight.

The "Blue-Yellow" Alternative. When in doubt, use blue and yellow (or orange). These colors are almost never confused by the majority of the population. There is a rare form called tritanopia (blue-yellow blindness), but it affects less than 0.01% of the population.

Final Audit.
Before you hit "publish" on that infographic or "deploy" on that new app feature, take 30 seconds. Toggle your Color Oracle or your browser extension. Look at your work. If it looks like a muddy mess of yellow and brown, go back to the drawing board. Your users—and your conversion rates—will thank you.

Critical Next Steps

• Audit your current brand colors: Use the Adobe Color Accessibility Tool to see if your primary and secondary colors conflict.
• Update your UI Kit: Ensure every "state" change (error, success, warning) is accompanied by an icon or a text label, not just a color shift.
• Install a system-wide simulator: Download Color Oracle today and keep it in your menu bar. Make it a habit to check every project at least once during the concept phase.