Many classic colour combinations in scientific presentations are inaccessible for colour blind readers. Here are five tips to make more inclusive choices when designing figures.
Figures are arguably the most critical part of a scientific manuscript. They are an excellent tool for visualising results coming out of a large amount of data. Indeed, many editors and reviewers first scan the figures before reading the text. So, frequently an editor or reviewer’s first impression of a manuscript depends on the figures’ quality and accessibility.
Unfortunately, some established scientific figure design features get in the way of that great first impression, because: Approximately 8% of men and 0.5% of women are colour blind. That means that approximately one in 12 male and one in 200 female reviewers – and ultimately readers – will stumble over figures with certain tone combinations. So, it is crucial to choose colour considerately.
This does not necessarily mean moving to the greyscale. According to the U.S. National Eye Institute complete colour blindness is relatively uncommon. Most types of colour vision deficiency mean difficulties to distinguish between certain colours. For instance, the most common type makes it hard to tell the difference between red and green:
Red-green colour blindness
With that in mind, here are five tips to create colour blind-friendly figures:
- Avoid the red/green combination
Red and green is a standard combination in heatmaps and fluorescence imaging. However, this pairing is particularly challenging for many people with colour blindness. An easy solution to this problem is moving to alternative two-tone combinations such as green/magenta, red/cyan, and yellow/blue.
- Use a colour blind-friendly palette
Several websites provide colour schemes that are colour-blind safe. For instance, the free web tool ColorBrewer offers palettes to delineate between up to nine different datasets. While designed for cartography, ColorBrewer simply shows you which colours work well together, so the information can easily be applied to graphs, etc.
- Use a single-colour palette
Different shades of the same colour – for instance sky blue to navy blue – work equally well. The only application for which I would advise against this option are line graphs as the lighter colours may be difficult to see when only applied to a thin line.
- Experiment with patterns and shapes
Another approach is developing figures that use patterns and shapes to distinguish between groups instead of colours. This works particularly well in scatter plots (with or without lines) in which you can choose differently shaped markers. Personally, I find that pattern fills look quite busy, so I avoid them. However, they are certainly a viable option.
- Test your figures
Several free colour blindness simulators can help evaluate whether your figure is accessible to readers with colour vision deficiency. For instance, I have used this web tool to convert the image above to the red-green colour blindness view. Another option is this downloadable software, which, however, I have never used.
I hope these tips are useful to you, and I wish you best of luck with designing your figures.