A yellow room makes us feel more cheerful (开心的) and more comfortable (舒服的) than a dark green one, and a red dress rings warmth and cheer to the saddest winter day. On the other hand, black is depressing (压抑). Light and bright colors make people not only happier but more active. It is a fact that factory workers work better, harder, and have fewer accidents when their machines are painted orange rather than black or dark gray.

Remember, then, that if you feel low, you can always brighten your day or your life with a new shirt or a few colorful things. Remember also that you will know your friends and your enemies better when you find out what colors they like and dislike. And don’t forget that anyone can guess a lot about your character when you choose a piece of handkerchief.

In February 2015, a photograph of a dress raised heated debate around the world. The disagreement centred on the dress’s colour: some people were convinced it was blue and black while others white and gold. People couldn’t understand how, faced with exactly the same photograph of exactly the same dress, they could reach such different conclusions.

For a long time, people believed that colours were objective, physical features of objects or of the light that was reflected off them. But this theory isn’t really true. Different wavelengths of light do exist independently of us but they only become colours inside our bodies. Every person’s visual system is unique and so are their perceptions (感知). This is why no two people will ever see exactly the same colours.

Another cause of the problem is language. People generally name only the colours they consider socially or culturally important. In English we divide colour space into 11 basic terms — black, white, red, yellow, green, blue, purple, brown, grey, orange and pink — but other languages do things differently. At least one Indigenous community has no specific words for any colours, only “light” and “dark”. The Aztecs, who were enthusiastic farmers, used more than a dozen words for green.

A single colour can mean completely different things in different places and at different times. In the west white is the colour of light, life and purity, but in parts of Asia it is the colour of death. Many people today think of blue as masculine (男性的) and pink as feminine (女性的), but only a hundred years ago baby boys were dressed in pink and girls in blue.

All of this taken together, it becomes rather difficult to reach a conclusion different from that of the 18th-century philosopher David Hume: colour is merely a phantasm of the senses.

First, all participants found it quite easy to link colors and emotions. This was particularly true for colors like red, black, or yellow. Other colors, like brown and purple, received fewer associations. We found that colour-emotion associations were not one-to-one, but many-to-many.

Participants did not select one emotion for a colour, but often chose several emotions. In turn, different colors were linked to the same emotion, like pleasure, which was associated with red but also yellow, orange, pink and purple.

What you can also see is that most colors were associated with positive emotions. Only brown, grey and black—that is, darker colors—were associated with negative emotions. Red was the most controversial colour. For some, it was a very positive colour—the colour of passion, love and desire. For others, it was a negative colour—the colour of danger, anger and hate. For even others, it was both positive and negative. What connects all these emotions and ideas is the fact that red is activating and strong.

Second, we found few cultural differences. In other words, many colour-emotion associations seemed universal. Most participants agreed that pink was associated with love and pleasure, yellow with joy and amusement, or that black was the saddest colour.

Third, if you are interested in cultural differences, we found some specificities too. For example, in addition to the universal associations of love and anger with red, Chinese participants also associated joy and amusement, while Nigerian participants additionally associated fear with red. Another example is the association between purple and sadness that only Greek participants chose. For others, purple was generally a positive colour with very little agreement on the exact emotions associated with purple.

Fourth, participants whose languages were more similar to each other also had more similar associations. To arrive at this finding, we estimated the degree of linguistic (语言的) similarity between two languages, which shows how related or unrelated they are. And then, languages from different language families, like English and Chinese, would have the lowest similarity scores.