Of course there will always be exceptions – the comment from the teacher saying “well done” is also written in red and raspberries are red, but perfectly edible. It is true that people do make different associations with different colours, but whether this translates into behaving in a certain way or succeeding at a particular task is a different question.

After so many mixed results in the past, in 2009 researchers at the University of British Columbia tried to clarify the situation once and for all. They sat their participants at computer screens coloured blue, red or “neutral” and tested them on various tasks. With a red screen people did better on tests of memory and proof-reading, tasks requiring attention to detail, but when the screen was blue they did better on creative tasks, such as thinking of as many uses as possible for a single brick. The authors speculated that red signalled "avoidance" and so they were more careful, while blue motivated the opposite: an "approach" behaviour that encouraged them to be freer with their thinking, resulting in more creativity. To test this idea, the researchers then asked the volunteers to solve anagrams of different words – relating to either avoidance or approach behaviours. The subjects tended to solve the avoidance words faster if they were presented on a red background, and the approach words more quickly if they were presented on a blue background – suggesting that the colours and behaviours were associated in their minds.

The team even speculated about the practical uses of their findings. For example, they wondered whether walls should be painted different colours depending on the task at hand – red for a team looking at the side effects of a new drug, for example, or blue for a room for creative brainstorming. In practice this might be tricky. In an office or a classroom you might want to think creatively some of the time and pay attention to detail at others.

Warning, or desire?

In any case, question marks are now hanging over the discovery itself. When another team tried to replicate the anagram part of the study with a larger group of people in 2014, the effect of colour disappeared. The initial study comprised just 69 people. In this new, bigger study, of 263 volunteers, background colour made no difference.

The same team also raised questions about another landmark finding, originally conducted by Oliver Genschow at the University of Basel in Switzerland. Genschow’s team had offered their volunteers a plate of pretzels, and told them to eat as many as they felt they needed to make a judgement about the taste.

Rather sweetly, one in six people had to be excluded because they were kind enough to share their pretzels with others which defeated the object of the research. But when that was taken into consideration, the colour red once again seemed to serve as a warning, and people offered pretzels from a red plate took fewer. Yet when the team from Appalachian State University followed the same procedure their results were the exact opposite – people with red plates ate more pretzels.

Pink prisons

Clearly, studying the effect of colour is much harder than it looks - or maybe colours just don’t have the effect that we expect. Yet we are convinced enough that they do for some prisons in the USA, Switzerland, Germany, Poland, Austria and the UK to paint their cells in a particular shade of pink. In Switzerland 20% of prisons and police stations have at least one pink cell. It’s a shade I’d call blancmange pink, but its proper name is Baker-Miller pink, after two US Naval officers who first studied the effects of pink walls on prisoners.

Back in 1979 prisoners were shown a blue card or a pink card and then had to try to resist the pressure of the experimenter pushing down on their arms. With the blue card they pushed harder, so was the pink card somehow reducing their aggression? Possibly not. The experimenter knew which card had been shown, so without even realising it they might have eased up a bit on the pink card. What’s more they had a trial run, followed by the pink card and finally the blue, so perhaps they were just more practiced when it came to the blue card. Several attempts to replicate these results in better-designed studies have failed. But they did follow up with an experiment conducted in real prison cells which were either white or pink, mixing a pint of red paint with a gallon of white to obtain this lovely shade. Once again the order of the colours was the same for everyone, so maybe it was the repainting of the cell that made a difference, rather than its pinkness.