Monthly Archives: October 2009

How many colours are there?

I sometimes begin a series of student lectures on colour with the question – how many colours are there? At least one student always answers: three! In fact, this week in my lecture when I asked this question the first three or four answers were all three.

I can see where the idea of three comes from since the number three is ubiquitous in colour. We have three different classes of cones in the retina of our eyeballs – each with maximum sensitivity at a different wavelength. As a direct consequence of this trichromacy we use colour monitors with three primaries (RGB), colour printers with three primaries (CMY – ok, sometimes black as well but there’s a good reason for that), and there is a misconception that there are three primary colours from whose mixtures it is possible to make every other colour – see

I think that the number of colours that we can see is about 10 million; maybe less, but certainly millions. However, there are arguments that the true number may be much greater than this. See, for example, Mark Fairchild’s article –

However, even the people thinking about colour mixing and three primaries must surely be aware that they have seen more than three colours. Indeed, were probably wearing more than three colours! So why do they respond with three? Well, it could be that they misunderstand the question and think I am asking about primaries (perhaps because they think the real question I am asking is too hard and nobody in their right mind would ask it). Or it could be that they equate the word colour with physical colorants. One of the most interesting – but also frustrating – things in field is that even the name of the field – colour – means different things to different people. Is colour something physical? Is it something you experience? Or is it simply whether something is red, yellow or blue etc; in other words, another term for what I would call hue?

This probably explains why we find the following text on this webpage –

A juvenile Mantis shrimp. These shrimps have the most complex vision systems known to science. Special light-sensitive cells allow them to distinguish between different types of polarized light, and they can see 12 colors (compared to three for humans) ranging into the near-ultra violet to infra-red parts of the electromagnetic spectrum.

It literally says that shrimps see 12 colours whereas, elsewhere on the page, it says that humans see 3 colours.  Despite this irritating lack of precision in the writing the article is quite interesting and describes the surprisingly complex nature of shrimp colour vision.


This is meant to be a serious blog. However, today is 31st October – Halloween. At least 50 children visited my house tonight – not all at the same time I might add – and each was given a small chocolate bar. I prefer the treat to the trick.

Given that it is Halloween I thought I would share the latest in Pumpkin technology – a remote controlled colour-changing pumpkin.








You can see a video of it in all its glory on youtube:

New Scientist colour quiz

New Scientist recently undertook an informal study to see if red is off-putting in a testing environment. 

They set up two quizzes, each consisting of the same 15 anagrams. One quiz was predominantly red and the other blue.

On every attempt to access the article, a pop-up appeared requesting that you take part in the test. The colour of the text and border of this box was randomly selected to be either blue or red, corresponding to the colour of the text and border of the anagram test to which it linked. They then gathered data on the click-through rate for both colours, and the relative success rate.

They got roughly the same follow-through rate for both colours – 8478 for red and 8550 for blue – so the colour of the pop-up did not seem to have an effect on how attractive a prospect it was to take part in the quiz.

They also found that the readers scored an average of 63 per cent in the quiz, irrespective of whether the text and boarder colours were red or blue.


the power of red

An interesting article in New Scientist has explored the influence of colour on the choices we make; how we act and think. The article – – quotes research published in Psychologial Science that revealed that the colour of clothing worn by competitors in a taekwondo contest affects the decisions even by experienced referees. In short, competitors wearing red were awarded 13% more points than those dressed in blue


This builds on previous research published in Nature in 2005 – – that showed that between 55% and 62% of bouts in Olympic combat contests were won by competitors wearing red when in fact red and blue should have won 50% each if colour had no effect. Robert Barton, from Durham University (UK) has argued that the colour red could influence the mind of the referee but could also affect the mental state and performance of the competitor.

Interestingly, 38 of the last 63 top division soccer titles in England have been won by teams in red (Manchester, United, Arsenal, Liverpool) and goalkeepers feel more confident about saving a penalty from a player in a white shirt than in a red one. Both of these facts were taken from papers published in Journal of Sports Sciences.

sustainable colour design

chromaticity diagram and RGB gamut

You may well have seen a typical diagram showing the chromaticity diagram and the gamut of an RGB monitor. The gamut is a triangle, of course, with the vertices formed by the chromaticities of the RGB primaries. See, for example,

However, that triangle is a little misleading. One problem is that we are only looking at the maximum chromaticities available – this does not imply that all of these chromaticities are available at every luminance level. Take the very vertices of the triangle – these occur for the RGB values [255 0 0], [0 255 0] and [0 0 255]. The luminance of the pure red [255 0 0]  might be 27 cd/m2, of the pure green [0 255 0] 56 cd/m2, and of the pure blue [0 0 255]  might be 6 cd/m2. (These are luminance values for a typical RGB monitor – your monitor will vary a little from this and depending upon your settings.) This means that the chromaticities of the points of the triangular gamut are only available at these respective luminance levels.

For the monitor just described the maximum luminance would be obtained when RGB = [255 255 255] and the luminance of this white would be 89 cd/m2. So for very high luminances the gamut is tiny since to achieve these high luminance values you need to have all three RGB guns firing and hence by definition the colour is going to be very desaturated.

For the typical monitor described above I have calculated the gamut of colours available at three luminance levels: 10 cd/m2, 40 cd/m2 and 70 cd/m2. I have plotted these below and coloured bright red the chromaticities that cannot be obtained at that luminance. So, for example, at 10 cd/m2 you can obtain most chromaticities but not the pure blue. The reason for this is the pure blue [0 0 255] would be only 6  cd/m2 – to get 10 cd/m2 you need to add a little red or green and this desaturates the blue.

At 40 cd/m2 you can obtain a much smaller gamut and at 70 cd/m2 the gamut obtainable is very limited. To get such high luminances on this typical RGB monitor you would need high R and G values and that gives you yellows and yellowish whites.

The point of all this is that gamuts are three dimensional and looking at the gamuts in a 2-D chromaticity diagram can be very misleading.














colour meaning

At some point I intend to post something about colour meaning or what I like to call colour semiotics. However, in the meantime you may like to refer to this blog entry – – about understanding colour for dress designing (though the advice seems quite generic and not connected with dress designing at all). It’s a reasonable primer into the meanings of colour.


I just came across this website –

The first version of Colorgorize was published in 2007 as a project at the University of the Arts Bremen, Germany. Back then, Colorgorize was a Firefox add-on that could display similar colored websites to the website currently opened. Colorgorize was changed to a website in 2009 to reach a bigger audience. Today, thousands of websites are already analyzed and can be searched by colors.

Colorgorize is essentially a site where you can get inspiration for web-design colours and palettes. It works by shrinking imags of webapages that can be organized according to your colour preference.

registration for CIC

Today is the last day you can register for the Color Imaging Conference in Albuquerque, New Mexico to qualify for the early-bird registration fee. This annual event is one of the foremost conferences in Colour Imaging and provides useful networking opportunities. The conference web site is