How to Simulate Color Blindness for Accessible Design

About 8 percent of men and 0.5 percent of women have some form of color vision deficiency. If your design relies on color alone to convey information — red for errors, green for success — a significant portion of your users will miss the message. A color blindness simulator shows you exactly what they see.

The four types of color blindness

The ToolStand Color Blindness Simulator uses Canvas LMS color space matrices to simulate: Protanopia — red-blind, most common. Reds appear dark or muted. Deuteranopia — green-blind, also common. Greens become brownish. Tritanopia — blue-blind, rare. Blues become greenish. Achromatopsia — complete color blindness, very rare. Everything appears in grayscale.

How to use the simulator

Upload a screenshot of your design, website, or app. Toggle between the four simulation types. Look for: elements that become indistinguishable (red and green buttons look identical under protanopia), information conveyed only by color (a chart where the legend is impossible to match), and insufficient contrast (text that fades into the background).

Fixing color accessibility issues

Add icons or patterns. A red error state should also show an X icon. A green success state should show a checkmark. Use sufficient contrast. WCAG 2.1 requires at least 4.5:1 contrast ratio for normal text. Label directly. Instead of "click the green button," label the button with text like "Submit" or "Confirm." Test with grayscale first. If your design works in achromatopsia mode, it works for all color vision types.

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