Colour is an extraordinary motivator. We sensibly caution against waving a red rag to a bull to avoid provocation – worthy but curious advice, since bulls cannot distinguish red from other colours.
We use red roses to signify romantic intention, yellow roses to affirm friendships and white lilies to share grief. While the role of these colours for humans may be culturally acquired, the reaction to colour among animals is largely “hardwired”.
In his influential volume The Study of Instinct (1951), Nobel Laureate Niko Tinbergen concluded that the red nuptial colouration of male three-spined sticklebacks acts as a signal stimulus for aggression by naïve and experienced males alike.
Red is used extensively to signify danger: red traffic lights warn us to stop, red flags warn of imminent dangerous weather or seas. Indeed, the apparently entrenched link between red and danger may explain the fascinating observation that colour can determine the outcome of combative sports.
During the 2004 Athens Olympics, contestants in wrestling, boxing and taekwondo were randomly assigned red or blue protective clothing. Russell Hill and Robert Barton showed that when the combatants were closely matched, those wearing red were more likely to win. Perhaps those wearing blue were intimidated, losing crucial points.
Animals also react cautiously to particular colours, including red, blue, black and yellow. Among the more notable are the dendrobatid poison-dart frogs and the brightly coloured ladybird and leaf beetles.
These “aposematic” colours represent warning signals to potential predators. The brightly coloured organism is either dangerous or unpalatable, possessing toxic chemical compounds that would adversely affect predators that failed to heed the warning.
Are humans also sensitive to such colours? The popularity of tomatoes, red capsicum and strawberries might suggest not. But recent experiments by Oliver Genschow, Leonie Reutner, and Michaela Wänke from the University of Basel indicate otherwise.
The research team wondered whether “warning” colours might moderate the consumption of “rather unhealthy” food, such as salty snacks or sugared soft drinks.
First, they asked a sample of young males to consume three flavours of soft drink, presented in clear plastic cups. The slightly yellow drink was flavoured with white tea, lemon or green tea. Each cup was identified with a lettered label, and the background colour of all three labels was either red or blue.
Remarkably, the students consistently consumed less soft drink from cups with red labels. This difference in consumption was not reflected in how the respondents scored the tastiness of each flavour.
While the students preferred different flavours (white tea was deemed the most and lemon the least tasty), they did not indicate the flavour was more or less appetising depending upon the colour of the label.
Genschow and colleagues found a similar pattern in food consumption. Male and female participants were invited to snack on pretzels as they completed a lengthy questionnaire. Ten pretzels were placed on either a blue, red or white paper plate.
Around three pretzels were consumed from the white and blue plates, roughly twice as many as that consumed from the red plate. Again, the subjects did not believe the colour of the plate made any difference to the taste of the food. In other words, there was no indication the drink or food tasted differently depending upon the colour of plate or label.
What are we to make of these data? The Basel team suggests the cultural and/or biological basis to the widespread association between red and danger causes the respondents to avoid consuming items closely associated with red.
While such an explanation has some appeal, the widespread consumption of red products, including fruit, vegetables, meat and wine, makes the link less certain.
Indeed, red can be emotionally appealing: not just red roses, but red dresses may signal romantic and sexual intent.
The surprising and remarkable sensitivity to colour revealed in these experiments has intriguing practical possibilities. Genshaw and colleagues initially wondered whether snacking behaviour – an obvious contributor to obesity – is influenced by background colour.
Their study suggests a way of reducing the consumption of particular foods or beverages, especially when it may not be possible to restrict their access: simply surround the offending food and drink with red.
But the effectiveness of this strategy depends on whether the aversive behaviour has a biological or cultural basis. If it’s the latter, a determined forager might just as easily learn to ignore the colour red as a deterrent.
Such reverse learning might be more challenging if the aversion is embedded in our genotype. Either way, it’s impressive that such simple differences in presentation can influence food and drink consumption, independently of how tasty the products may seem.
My thanks to Mandi Tong for alerting me to the original article and her subsequent insightful conversations.