See your image the way colorblind users do

Why designs need a color blindness check

Color vision deficiency affects roughly 1 in 12 men and 1 in 200 women worldwide, most commonly as difficulty distinguishing red from green. If a chart uses only red and green to mean "bad" and "good," or a button's status only changes color and nothing else, a meaningful share of visitors simply can't read that signal. This tool lets you preview an upload the way several common types of color vision deficiency would actually render it.

The four types simulated here

• Protanopia — reduced sensitivity to red light. Reds appear darker and can be confused with black or dark green.
• Deuteranopia — reduced sensitivity to green light. This is the most common form, and it makes reds and greens hard to tell apart in a similar way to protanopia but with a different underlying cause.
• Tritanopia — reduced sensitivity to blue light, much rarer than the red-green types. Blues and yellows become difficult to distinguish.
• Achromatopsia — complete color blindness, seeing only in shades of gray. This is rare, but it's a useful stress test: if your design still communicates clearly in grayscale, it isn't relying on color alone.

What to do if something fails

The fix is rarely to change your whole palette. Add a second signal alongside color — an icon, a pattern, a label, an underline — so the information doesn't depend on color perception alone. For charts specifically, distinct shapes or line styles per series work well alongside, or instead of, color coding.

Using the contrast checker alongside the simulation

Low contrast and color vision deficiency are separate problems that often show up together. A color pairing can have enough contrast for someone with typical color vision but still fail for someone with a color vision deficiency if the two colors sit close together on the confusion lines those conditions create. Check both: run the simulation to see if two colors become visually similar, and use the contrast checker to confirm the actual luminance contrast meets WCAG guidelines.

Frequently asked questions

Is this simulation scientifically exact?

It uses well-established color transformation matrices that approximate each condition closely enough for design decisions, though individual experiences of color vision deficiency vary in severity and this isn't a substitute for testing with real users.

Can this diagnose color blindness in a person?

No — this simulates how an image would look to someone with a color vision deficiency. It doesn't test a person's own vision. An eye care professional can do that.