Free Tool

Colour Blindness Simulator

Upload any image to see how it appears to users with different types of colour vision deficiency. Essential for WCAG 1.4.1 (Use of Colour).

What is this?

This tool shows you what your website looks like to people with different types of colour blindness. Around 1 in 12 men and 1 in 200 women have some form of colour blindness.

When do I need this?

Use this when reviewing your design or when checking whether you rely on colour alone to convey information (e.g. red = error, green = success). If the meaning is lost in the simulation, you need to add an icon or text label.

Applies to:All websites and apps with colour-coded information, charts, maps, status indicators, or form validation.
  1. 1
    Enter your page URL or upload a screenshot — Type the address of the page or upload a screenshot.
  2. 2
    Select a colour blindness type — Try Deuteranopia (the most common type) first, then Protanopia and Tritanopia.
  3. 3
    Check colour-only information — Look at error messages, success states, charts, and maps. If the meaning disappears or is ambiguous, you have an issue.
  4. 4
    Identify fixes needed — For anything that relies on colour alone, add a text label, icon, or pattern. For example, add an ✗ icon to error messages alongside the red colour.
  5. 5
    Export your evidence — Download the simulation screenshots for your Technical File.

WCAG 1.4.1 — Use of Colour

Colour must not be the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. Use shape, pattern, or text labels alongside colour.

Export as evidence

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Legal basis:EAA Act — Annex I →

Every export includes a legal-evidence metadata footer with the audit ID, generation date, tool version, EN 301 549 clauses, and the standard disclaimer. Legal-grade evidence — not legal advice.

Simulation method

Colour vision deficiency simulations use colour transformation matrices based on the Viénot, Brettel, and Mollon (1999) simplified model. Results are perceptually representative for design review purposes but may differ from higher-precision spectral models (e.g. Machado et al. 2009). Use for design review and accessibility checking — not clinical diagnosis.