Categories of colour are not born of language but are rooted in biology, according to research that shows babies divide colours up into red, blue, green, yellow and purple.

Humans see colour as a result of cells in the eyes known as cones, which are sensitive to either long, short or medium wavelengths of light. The way in which the brain interprets combinations of signals from these cells allows us to see a whole spectrum of colour.

But whether biology underpins the way in which we label colours has been a matter of debate.

While babies have previously been shown to have some colour categories, different languages have different groupings – some do not separate green and blue, for example – suggesting categorisation of colour might be down to culture.

“We wanted to find out what’s the connection between the two, what is it that babies are using to make their colour categories and what can that tell us about the way we talk about colour as adults,” said said Alice Skelton, first author of the research and a doctoral candidate at the University of Sussex.

Writing in the journal Proceedings of the National Academy of Sciences, Skelton and colleagues describe how they tackled the conundrum by analysing the response of 176 babies, aged between four and six months, to patches of colour.

Each infant was seated in front of a wooden booth which had two windows side by side, and was recorded using a webcam.

Both windows were repeatedly filled with the same colour, after which one of the windows was filled with a different hue at random. The new pairing was then shown multiple times. Each baby was shown only one pair of different colours, with at least 10 babies tested for each pair.

From the webcam recordings, the team looked for a phenomenon known as novelty preference: babies will look longer at a “new” colour if they perceive it to be different to a familiar one. If a baby looks consistently for longer at the new colour – even if it is next to the other on the colour spectrum – it suggests the colour is perceived as belonging to a different category.

In total, 14 different colours of the same lightness were used, spanning the colour spectrum. While some infants were shown pairs of colours very close to each other, others were shown pairs slightly further apart to probe where the babies’ boundaries fell for colour categories.

The results revealed that babies have five colour categories: red, yellow, green, blue and purple. The team then compared these colour categories to those found in English, and to 110 languages from non-industrialised countries.

While different languages have different numbers of colour categories and different locations for the boundaries between them, the common categories aligned well with the babies’ categories.

Furthermore, four of the infants’ colour boundaries were found to map to the four extremes produced by signals from different cone types when they are combined and interpreted by the brain.

Together, the team says, the results suggest there is a biological origin to colour categories, which is later influenced by culture and environment.

“If you [use] a language that doesn’t make a distinction between green and blue, for example, then as they grow up babies and children learn to no longer make that distinction.” said Skelton, adding that research should now explore how our categories shift as we develop language.

Delwin Lindsey, professor of psychology at Ohio State University who was not involved in the work, described the study as a tour de force.

“These results are important because they strongly support the view that the universality of colour categories seen in world languages has a biological origin, since colour categorical structure is demonstrated long before infants ‘learn’ their native words for the colour categories,” he told the Guardian.

Asifa Majidof Radboud University in the Netherlands also called the research exciting.



“This [new study] is adding to a solid body of work showing that babies, before they have learned any kind of mastery of their language, are already busy [making] the building blocks of the concepts that they are going to have,” she said.



But, said Majid, it is still possible that the colours that babies are surrounded with from birth – for example in baby toys – could be preconditioning them to categorise colours in a particular way, addingthat the study should be repeated with babies from different cultures to explore whether the five categories are truly ubiquitous.

Others pointed out that the colour spectrum used only included a limited number of highly saturated colours, the biological mechanisms proposed only explain four of the babies’ five colour boundaries, and that the findings do not explain the ease with which infants learn additional categories, such as orange.

With the debate ongoing, Majid believes the study is likely to stir debate. “This is going to blow a lot of people’s minds,” she said.