How many colors are there?

It sounds like a very simple question but the answer is far from simple. It’s commonly agreed that there are seven colors in a rainbow. They are red, orange, yellow, green, blue, indigo and violet. If you ask the Crayola Company, the people who make crayons, they’ve got 120 different colored crayons in their range. The HTML language, which describes web pages, has got 121 uniquely named colors that we can use. Many Unix-based operating systems, for instance, the very popular Linux operating system, have a windowing system called X11, and X11 distributions come with a file called RGB.text, which lists a whole bunch of different colors, and the last time I looked at this file it contained 881 different colors.

If you look at a collection of all the words in the English language, what they call the English Corpus, there are around 4000 different words that we use to describe colors.

Another simple question that’s got a complex answer is ‘where does one color end and another color start?’. So over here we can see a figure which contains a range of colors from reds, yellows, greens, blues, and so on. And in a recent exercise they surveyed a large number of web users, 1.5 million web users, and asked them to draw boundaries between the different colors, and to name them. And this is a consensus across 1.5 million web users. It shows what people tend to agree as being green and what they think is blue and what they think is teal and so on. This is difficult because we’re trying to delineate regions in color, and color is a continuum, and we’re trying to enforce sort of arbitrary boundaries across this otherwise continuous notion of color.

The way we interpret color also depends on our cultural background. In Asia, orange is a very, very positive color, but in the United States, Australia and parts of Europe, orange is considered to be a color of danger or of hazard. Some African languages, for example, do not have any words which distinguish the color red from the color orange. However, all of the languages have got words to describe black and white, and if the language has got more colors than just those two, the next most likely color that they are going to describe is red, and next most likely is either yellow or green. Blue is frequently the sixth named color in many languages, so blue really is not as important as red and green, black and white. Brown comes later and then all of the other colors that we’ve got names for.

This rather complex graph shows a relationship between the culture, which is indicated by the letters here, and the emotion, which is indicated by the radial color bars, numbered from 1 through 284. What we can see is the very different colors that are used to represent different emotions or feelings across cultures.

If we look at the occurrence of color terms in a big collection of English words, for instance, the Bank of English Corpus contains a lot of literature from the United States, United Kingdom, and Australia for example, then we could look at a histogram of the occurrence of those color words. And we see that black is by far the most frequently occurring word, followed by white, followed by red, green blue and so on, whereas the least occurring words are those like ultramarine and chartreuse.

The most common color words are also the oldest. So 1200 years ago there weren’t that many different color words but as time has passed we’ve introduced more and more color words into our vocabulary. There’s a big transition point around the year 800, where we changed from a focus just on brightness, talking about white, black, grey and so on, where we started to get more interested in talking about the hue, the actual color, rather than just the brightness. Perhaps this was a technological transition as well, perhaps when dyes and pigments became much more common.

The Pantone company’s whole livelihood is based on color. They catalogue colors, they describe all of the colors using unique numeric codes, and they promote every year a color of the year. So the color of the year in 2013 is this green.

The bottom line is that color is really, really important to humans.


There is no code in this lesson.

Color is a very important concept for people. We have lots of words to describe colors and we even associate them with emotions.

Professor Peter Corke

Professor of Robotic Vision at QUT and Director of the Australian Centre for Robotic Vision (ACRV). Peter is also a Fellow of the IEEE, a senior Fellow of the Higher Education Academy, and on the editorial board of several robotics research journals.

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