How to check your colours for colour blindness

The best way to check colours for colour blindness is to look at your own design through a simulation, and Paint by Zaweba has one under View > Proof Setup > Simulate. It previews protanopia, deuteranopia, tritanopia and achromatopsia over the live document, so you can see how a chart, map or button will look to someone with each type, then fix problems before anything is printed or published.

Colour vision deficiency is common, especially among men, and most of it involves telling reds and greens apart. A design that relies only on red versus green to mean stop versus go, or loss versus profit, can leave a lot of people guessing.

What the four simulations show

Protanopia is reduced sensitivity to red light; reds look darker and can be confused with greens and browns. Deuteranopia affects green and is the most common form; reds and greens become hard to tell apart. Tritanopia is rarer and affects blue, making blues and greens and yellows and pinks confusing. Achromatopsia is seeing no colour at all, only light and dark, which is also a useful test of whether a design works in greyscale.

Step by step with colour checks

Open your design and choose View > Proof Setup, then Simulate, and pick one of the four. The canvas changes to the simulation while your file stays untouched. Work through each in turn and look for anything that carries meaning through colour alone: lines on a chart, coloured status labels, a map key, buttons in a game interface.

Turn the simulation off again from the same menu. It's a preview, not an edit, so there's nothing to undo.

Fixing what you find

If two colours merge in a simulation, change their lightness, not just their hue. A dark red and a light green stay distinguishable to almost everyone because they differ in brightness. Keep the colours you like, but push one lighter and one darker until they separate in every simulation.

Don't rely on colour alone. Add labels to chart lines, patterns or textures to areas on a map, icons or words on status badges. Then colour becomes a bonus rather than the only clue.

Check contrast for text. Achromatopsia mode is a quick way to spot low contrast: if text nearly disappears into its background in greyscale, it will be hard to read for many people, including anyone with tired eyes or a dim screen.

The same menu helps with print

Proof Setup does more than colour blindness. It soft proofs a CMYK or RGB profile so you can see how a picture will print, Gamut Warning greys out colours the press can't reach, and you can view the C, M, Y and K plates on their own. A Soft Proof adjustment layer is there too. Checking for colour blindness and print in the same pass is a sensible habit for posters and leaflets.

When to check

Check early, when the colour scheme is first chosen, and again at the end. Changing a palette at the start costs nothing; changing it after fifty slides costs an afternoon.

Paint by Zaweba is free and works offline on Windows, so you can test client work and private designs without uploading them to an online simulator.