How many colours do you need to visualise data scored on a five-point scale?
If you went with the obvious answer of five colours, here’s what you get:
The green and grey figure wins in two ways. First, it tells a story: about a third of respondents view Wikipedia favourably. (Although there are other interpretations of the data shown, a good figure emphasises a single message.) Second, the grey and green version just looks better.
Jet was a ubiquitous colourmap that slowly fell out of fashion over the last five years. It was the default colourmap for Matlab and Matplotlib (and probably others) until 2015ish. The replacements, Parula and Viridis, respectively, get a lot of love. A quick Google search will present numerous blog posts and articles maligning Jet and promoting the use of these newer colourmaps. It’s an unpopular opinion but, especially now that they are common and overused, I dislike Parula and Viridis as much as I dislike Jet.
When designing any figure with colour, consider the Hue-Saturation-Lightness (HSL) colour space. It is the most intuitive and simplest colour space to work with. For examples of why it is well suited to scientific figures, skip to the bottom. To learn the details, read on.
Colour figures in journal articles are common these days. Many of the people reading them, however, will print them in black and white. Consequently, when designing figures, we should ensure they remain meaningful if converted to grayscale. Here are a few tips to keep in mind.
Far too often in scientific publications, the choice of colourmap for a figure has been given no thought. How do I know? Because every colour in the rainbow has been used.
For some reason rainbow colourmaps are the default in many programs, despite them being inappropriate for countless situations. I am not the first to recommend never using the rainbow/jet/hsv/etc… colourmaps, but apparently it needs repeating. If I arbritrarily pick a journal and go to the most recent articles, I am bound to come across multiple instances of these awful colour schemes.