Why it matters
About 1 in 12 men and 1 in 200 women have a colour vision deficiency. Most have difficulty with reds and greens, which is exactly the pair most dashboards, forms and maps use for good and bad.
WCAG 1.4.1 says colour must never be the only way information is shown. The easiest way to check is to look at the design the way an affected visitor would. This simulator uses the Machado, Oliveira and Fernandes (2009) model, widely used in design and research tools, and checks every pair of colours in your palette for ones that merge.
How to use it
- Choose a screenshot or use the sample photo to see all four simulations side by side.
- Lower the severity to see the milder forms, which are more common than full colour blindness.
- Paste your palette, one colour per line, to check every pair.
- Where colours merge, add a label, pattern or icon as well as the colour.
FAQ
How accurate is the simulation?
It's a well-established model of average vision for each type, not an exact copy of any one person's sight. Use it to find problems, then fix them with labels and patterns rather than tuning colours to the simulation.
What does the severity slider do?
100% is full protanopia, deuteranopia or tritanopia. Lower values blend towards normal vision to approximate the anomalous forms, such as deuteranomaly, which is the most common type.
What is achromatopsia?
Seeing no colour at all, only brightness. It's rare, but the same view shows how a design looks in greyscale or on a monochrome display.
Is my screenshot uploaded?
No. It's processed on a canvas in your browser.
