About 1 in 12 men and 1 in 200 women of Northern European descent have some form of colour-vision deficiency, most often difficulty telling red from green. In a room of reviewers, readers or conference attendees, someone almost certainly sees your figure differently from you. A colour-blind-safe figure costs nothing extra and makes sure your main message reaches everyone.
The common problems
- Red vs. green as the only difference: “up” in red and “down” in green, or green and red fluorescence channels, can look identical.
- Rainbow colour scales: they create false boundaries and break down for colour-blind readers. Single-hue or perceptually uniform scales (such as viridis) work better.
- Colour carrying all the meaning: if two pathways differ only by colour, readers who can’t separate the colours lose the story.
A safe starting palette
The Okabe–Ito palette was designed to stay distinguishable for the common types of colour-vision deficiency, and was popularised for scientific figures by Bang Wong’s Nature Methods column:
| Colour | Hex |
|---|---|
| Orange | #E69F00 |
| Sky blue | #56B4E9 |
| Bluish green | #009E73 |
| Yellow | #F0E442 |
| Blue | #0072B2 |
| Vermillion | #D55E00 |
| Reddish purple | #CC79A7 |
| Black | #000000 |
For two-channel images, magenta and green are a common safe replacement for red and green.
Four habits that fix most figures
- Add a second cue. Pair colour with shape, line style, pattern or a direct label, so meaning survives without colour.
- Vary lightness, not just hue. Colours that differ in lightness stay distinct for almost everyone, and in greyscale print.
- Label directly. Put labels next to the elements instead of relying on a colour-coded legend.
- Test it. Adobe Illustrator and Photoshop can preview protanopia and deuteranopia (View → Proof Setup), and free tools such as Color Oracle simulate colour blindness across your whole screen.
Want your figure checked?
Send me your current figure for a free figure check: three concrete fixes, including colour accessibility, no obligation. Every figure I design can be built on a colour-blind-safe palette on request.
Further reading
- Wong B. Points of view: Color blindness. Nature Methods 8, 441 (2011).
- Okabe M, Ito K. Color Universal Design (CUD): how to make figures and presentations that are friendly to colorblind people (2002).
