Is it time scientists abandoned rainbow?

If you are a climate scientist or marine scientists or almost any type of scientist, then you are almost certainly familiar with the famous colour scheme called rainbow. It is one I have used in a recent paper. I reproduce a figure below.

It is also a colour scheme I use throughout my recently finished thesis. (Let’s just say you need more than two hands to count the number of times it appears. Though, thankfully I have now decided to stop using projected maps, which quite simply don’t work in R)

So, I am probably inclined to be resistant to calls this week in Nature to stop using it. Hawkins et al. have a rather provocative piece of correspondence in this week’s Nature, called “Graphics: Scrap rainbow colour scales“.

It’s a short piece, but here’s an excerpt:

It is time to clamp down on the use of misleading rainbow colour scales that are increasingly pervading the literature and the media (see http://tiny.cc/endoftherainbow). Accurate graphics are key to clear communication of scientific results to other researchers and the public — an issue that is becoming ever more important.

Aside from the challenge they pose for colour-blind readers (S. C. Allred et al. Nature 510, 340; 2014), spectral-type colour palettes can introduce false perceptual thresholds in the data (or hide genuine ones); they may also mask fine detail in the data (D. Borland and R. M. Taylor Comput. Graph. Appl. 27, 14–17; 2007). These palettes have no unique perceptual ordering, so they can de-emphasize data extremes by placing the most prominent colour near the middle of the scale.

I am inclined to half agree and half disagree. Let’s begin with what I think is the key problem with their argument. The use of rainbow has now become a convention in many areas of science. In some fields, such as what I am currently working on, it is more or less universal. And I would argue that anything that departs from rainbow is actually more difficult for researchers to understand than rainbow itself.

The other problem with the arguments of Hawkins et al. is that they are essentially calling for scientists to spend a huge amount of time inventing ad hoc colour scales. For example, read their first piece “An open letter to the climate science community.” Under the heading “What are the possible solutions?” they provide some helpful guidance, but nothing particularly universal. And that’s what is needed a relatively universal colour scheme, or 3 or 4 colour schemes that will become conventions within science.

Until then, I am skeptical that discarding rainbow is a good idea. Why replace a slightly flawed graphical convention with utter chaos? After all, consistency is at the route of good style.