Today I recorded by fourth video on the Colourchat youtube channel. You can see the video here.
I started with a very difficult question – where is colour? – which ended up having to be recorded in two parts. So it was somewhat of a relief to record this easier question – is black a colour?
That said, there are those who argue black is not a colour. There are also those who argue that black is the absence of colour or even the absence of light. I briefly discuss all of these issues in my video.
In short, I think that black is a colour, albeit an achromatic one. It is definitely not a good idea to define black as the absence of colour of the absence of light. Anyway, watch the video if you are interested and let me know if you agree with my view.
Over the last year or two I have not posted as often to Colourchat as I would have liked. I have posting here for over ten years believe it or not. There are a number of reasons why I have been less active here just lately. One is that I have posted a lot on quora. And my posts on quora get more views than my posts on my own blog. And it is always nice to reach more people. On quora I don’t just write about colour. In my top-4 most read posts there one is about whether you need to be intelligent to get a PhD and one is about blindfold chess.
It’s slightly mad that my post about the attributes needed to undertake a PhD has about 1.2 million views – that is about 1.2 million views more than my most-read academic paper.
I have also been very busy over the last year working on a new book with Maggie Maggio. More of this later, but you can see the book here.
But another project I have been quite busy with has been The Colour Literacy Project. We started meeting before COVID actually and we all share a frustration that there is quite a lot of misinformation out there about colour. And a lot of people have misconceptions. At the end of the day, colour education leaves quite a lot to be desired in my opinion. So I am really happy to share the Colour Literacy webpage on colour misconceptions. You can see this here.
My contribution to the misconceptions page is actually rather minor. There are others in the Colour Literacy Project who have made much more valuable contributions than me. But the most important thing is that this page exists. It is, in my opinion, a brilliant teaching resource and I will certainly be directing my students to it when teaching starts this autumn at University of Leeds. Please take a look at it. Let me know if you agree with the misconceptions or if there are any misconceptions that you have come across that are not yet listed.
This week we hosted our second Leeds Colour Conference following the successful event in 2019. You can see details of the event here. We had two keynote speakers who didn’t disappoint. The second keynote was given by Ján Morovič from HP who spoke about how many colours there are. It was a brilliant presentation. Not surprisingly, there was no single answer. Rather, Ján’s talk discussed why this is a difficult question to answer and why there is probably no precise answer. But in doing this he covered so much ground in his usual engaging style. It was by far my favourite talk of the conference.
However, his talk reminded me of something I posted on quora a year or so ago. My post was not as sophisticated as Ján’s talk of course but covers some related topics. I reproduce it below for your reading pleasure:
HOW MANY COLOURS ARE THERE IN THE UNIVERSE?
This is a really interesting question but it cannot be answered without first stating what colour is.
I teach colour science at the University of Leeds. Whenever I have a new class I invariably start with the question: how many colours are there? (in the universe, is implied and sometimes I explicitly add, in the universe).
Within the first five minutes someone normally says that there are about 16 million; another person will say that there are an infinite number; and someone else will normally add that there are only three colours? Sometimes, I get someone who says that there are no colours (in the universe).
I then ask them how many countries there are in the world. Undergraduate students generally don’t know and to be fair I had to look it up. It turns out, of course, that the number depends upon whether you accept this or that country as being an independent country. However, the answer is about 186. Students normally give answers close to 186. Some may go as high as 300 and others as low as 150. But nobody says that there are as few as three. We don’t get answers to this question that range from 0 to infinity? Why?
The reason is because when we use the word country we have a good shared understanding of what the word means. When we use the word colour we do not. So that is where we need to start.
I think the two most logical answers are that there are zero or infinity. But let’s deal with 16 million and 3 first.
Those who say that there are about 16 million colours are aware that there are about 16 million different combinations of RGB on a typical emissive display. However, this is an arbitrary constraint of current technology, actually of commercial technology. When I was studying for my PhD (in the 80s I might add) I was not aware of any display that could provide 16 million combinations of RGB. We were happy with about 16. But in my lab today I have a display (actually the combination of a display and a graphics card) that can display about 1 billion different combinations of RGB. 24-bit colour displays (that can display RGB each with 256 values) are common. There doesn’t seem to be a consumer demand for displays with higher bit depth. But such displays certainly do exist and are used in research labs all over the world including in my own.
Those who say that there are only three colours in the world are referring to one of two ideas, both of which are fallacies. The first fallacy is that we can generate all colours by mixing three colours (called primaries) together. Of course, it has been known for a very long time that we cannot mix three colour primaries together to make all other colours. We cannot do this irrespective of whether we use additive or subtractive colour mixing. We can make all hues but hue and colour are not synonyms. If we try to make all colours by mixing three primaries we will find that we cannot match the chroma or saturation of some of the colours in the world. The second fallacy is that our visual system sees the world in RGB and creates all other colours from that starting point. This is ridiculous of course. Not only do we not see the world in RGB but it is not even true that we have three cones that are sensitive to just red, green and blue. I’m not going to provide a full explanation about this here but I have written about this quite a lot before. I will simply show the spectral sensitivity of the three cone types we have in our eyes.
Notice that the L cone class (which is sometimes referred to as the R or red cone) has sensitivity to (and therefore responds to) almost all of the visible wavelengths and that the maximum sensitivity of this cone is not even in the red region of the spectrum.
Now we can come to the idea that there are an infinite number of colours in the world. This idea is based on the belief that colour is a physical property of the world. According to this view, light at say 700nm really is red. It doesn’t just look red, it is red. This idea has been contested for a very long time. The earliest critique of this that I can find is by Democritus (460–370BC) who said:
For by convention colour exists, by convention bitter, by convention sweet, but in reality (there is only) atoms and the void.
According to this alternative view, perceptions such as colours, sounds, and smells do not exist in the world independently of us or other sentient beings. Imagine a world where there is no living sentient creature. A tree falls in the forrest. Does it make a sound? When the tree falls it generates a movement in the air called a pressure wave. It is only when that wave strikes the intricate structures of our ear that a physiological response is generated that ultimately results in our brains generating the perception of sound. Similarly, we touch a hot metal object. We experience pain. We would say that the pain is a property of the object. We experience the perception of pain which is our response to a physical property of heat. Sound is something that we experience as a response to a physical property (movement of air). Taking this view, we can say that colour is a response to sensing the physical property of light. Democritus is perhaps less well known than Newton who wrote something similar in the 1700s. He said:
For the rays to speak properly are not coloured. In them there is nothing else than a certain power and disposition to stir up a sensation of this or that colour.
According to Newton, light at 700nm is not red; it merely looks red to us. This might seem to be splitting hairs but the distinction is critical. It is why we sometimes disagree about a diagram similar to the one shown below.
The two small squares above are physically the same. You are probably looking at them now on a display. These two squares have the same RGB values. However, they don’t look the same. I quite like to use the terminology physical and perceptual colour (though I note that not every colour expert will agree with this classification). I would argue that the two squares are physically the same colour but perceptually different colours. The one on the right looks lighter, for example.
Some people will say that this is an illusion and they will say something like this.
The two squares are the same colour but they look different in colour because of the contrast with the respective backgrounds.
In fact, this is the view of most laypeople, I would argue.
However, it is my opinion that when they say something like this they are using two different definitions of the word colour in the same sentence without realising. I would modify their sentence to make this clear as shown below:
The two squares are the same (physical) colour but they look different in (perceptual) colour because of the contrast with the respective background.
They are some striking examples of this sort of illusion. For example:
In this image, the blue squares on the upper surface of the cube on the left are physically the same as the yellow squares on the upper surface of the cube on the right. By physically the same I mean that they have the same RGB values if you are looking at this on a display. If you print out this image and cut out the respective blue and yellow patches and view them out of context they will appear grey. In fact, the printer will have simply used a little bit of black ink in order to generate these blue and yellow patches. So where is the colour coming from?
I am happy to accept the terms physical and perceptual colour even though I have close colleagues who do not agree with me. They would argue that colour is perceptual and that there is no physical colour; there is only light. They would argue that light at 700nm, for example, is not red; it merely looks red. And they would have the likes of Democritus and Newton on their side.
If we accept for a moment that colour is a physical property then I think we could argue that the number of colours in the world is infinite. At least, for any practical purpose. I’m not an expert in quantum phenomena.
I have worked for my whole life to try to understand colour and to solve practical problems that arise in connection with colour. I work at the University of Leeds where I am Professor of Colour Science and Technology. In addition to my teaching and research I have undertaken consultancies with companies. These companies are concerned with textiles, automotives, food stuffs, cosmetics, dentistry, skincare, displays, printers, paints, inks to name but a few of the topics. You see, everything in the world that is manufactured is coloured and companies who manufacture those things invariably start to worry about how we communicate colours, how do we control colour, and how do we assess colour. And that is where I come in. In the 35-40 years of my professional career I have never come upon one instance of a company who cares about physical colour. They care about what colours look like. Because that’s what their consumers care about. Imagine a scenario where a consumer buys a suit and the jacket and the trousers don’t match. They look different in colour. And imagine that when they take the garment back to the store to complain the customer service agent says, “Don’t worry. They are the same physical colour. It’s just an illusion that they look different in colour.” It just won’t wash (pardon the pun).
Whenever I talk about colour or write about colour I am referring to perceptual colour. For me, if two things look different in colour, they are different in colour because that is how I define colour.
So finally we get to the people who responded that there are no colours in the world. They understand that colour is perceptual. They may even say that colours don’t really exist. However, I would disagree with them on this last point. To argue that colours don’t exist because they are perceptions is akin to arguing that pain is not real or that love does not exist. Not everything that exists in this world is explicitly physical.
Can a display with 16 million RGB combinations display 16 million colours? If you believe in the physical definition of colour you would presumably say yes. I would say no. Some of these combinations of RGB produce colours that are indistinguishable. According to my view of perceptual colour, if two stimuli (sorry to be technical at this point but if you have read so far I think you will allow me this) look the same colour, they are the same colour. And if two stimuli look different in colour they are different in colour. A while ago I published a paper that attempted to determine how many colours a smartphone could display. I ended up with an estimate of 2–3 million. I should declare that this work was supported financially by Samsung. But I still think the methods are interesting.
If you ask colour scientists in the world how many colours there are, most will say that this boils down to how many colours we can discriminate between. However, this is still a very difficult question to answer. And I have at least one close friend (who is a world expert in colour) who would argue that the question is ill-posed and cannot be answered. However, most estimates put the number somewhere in the range 3–8 million. My answer would be 3–5 million.
So there we have it: there are 3–5 million colours in the world.
You may agree or disagree with me. However, I hope – at the least – that you will agree that the question of how many colours in the world is an interesting and complex one. There is no easy answer that everyone agrees with. Certainly, it depends upon how you define the word colour. In my opinion, a lot of the disagreements that we see about colour stem from this problem that we don’t have a shared understanding of what the word even means. Some people, as I mentioned earlier, even conflate the words hue and colour and that is one of the many reasons why there are so many misconceptions around today about colour such as the fallacy that we can make all colours starting with three primaries.
Postscripts:
I post a lot on quora – mainly about colour but sometimes about other subjects such as academic and chess. If you want to read any of that you can see my quora page here.
Quora is free and I have no intention to ever participate in the quora program that monetises content. I really love quora as a platform. I have met some really nice (and incredibly knowledgeable) people there. The only thing that could make me leave quora would be if it becomes completely overrun with chatbots (thinking about it, that could be happening quite soon). But I do provide some paid content on a different site. A while ago I set up a patreon website where for a small monthly contribution you can get more focussed, detailed and intimate content. The idea behind this is to to generate ad curate high-quality content that will help people on their journey to understand colour.
If the idea of people conflating terms such as hue and colour intrigues you and you are interested in more such misconceptions I really encourage you to visit the Colour Literacy Project webpage and particularly to view their new page on colour misconceptions.
This week we had a three-day colour conference at the University of Leeds. You can see details of it here. This follows on from our successful event in 2019. COVID meant that it took 4 years to host our second conference but hopefully it won’t take so long for the next one. We had so many excellent speakers but one of these was Dimitris Mylonas (pictured) from Northeastern University London, UK who spoke about Colour Naming in Humanity-Centred Design. Dimitris is one of those people whose work I admire but I don’t get much chance to meet him even though we both live in the UK. I particularly like the use of on-line experiments in his research.
Last night I was chilling after the event finished and browsing youtube and I came across this interesting youtube video about the origins of English colour words. It is definitely worth a watch. It includes the idea that some ancient cultures didn’t have a word for blue and that they couldn’t see blue. Although I think it is true that they didn’t have a name for blue I am less convinced that they couldn’t see blue. As evidence for this people often cite Homer’s description of the sea as being wine dark in both the Iliad and Odyssey. If only I had seen this video the day before it would have reminded me to ask Dimitris what he thinks about this. I am sure he would have had something to say.
There was an interesting article in The Guardian today about a new blood test that can detect whether someone is sleep deprived. The idea is to use it to prosecute drivers involved in accidents who have had less than 5 hours sleep. According to the article driving after less than 5 hours sleep is as dangerous as driving after drinking alcohol. Experts are divided on the ethics of this.
This was particularly interesting for me for two reasons. Firstly, because this time last week I was on a flight from Manchester to LHR, en route to Texas where I took part in a couple of panel discussions about colour psychology having gone to sleep at 11:30pm the night before and left the house at 3:30am after fitful sleep for less than four hours. During the 1.5 hour drive from Leeds to Manchester in the early hours I had felt completely awake; however, I wonder whether I would be able to make this journey in a few years if the legislation is introduced.
But secondly, because my own research is concerned with the effect of light sleep and the devastating effects that lack of sleep can have on our health and wellbeing. A discussion about this topic actually came up during the Texas trip. I would encourage everyone to listen to Matt Walker’s superb TED talk – Sleep is your super power. We now know that light plays a crucial role in maintaining a healthy sleep schedule. Healthy sleep is entrained by exposure to bright light in the few hours after waking and to lack of exposure to light in the hours before going to bed. There is debate about the relatively importance of the light being blue. The light-sensitive cells in the retina that are implicated in sending signals to the hypothalamus in the brain (from where the release of hormones is controlled) are maximally sensitive to light at about 480nm but there is some evidence that longer wavelengths of light could also influence alertness (in other words, the cones may also be involved). Here is one of my own papers on this topic:
Lin J & Westland, 2020. Effect of long-wavelength light on electroencephalogram and subjective alertness, Lighting Research and Technology, 52 (6), 763-774.
There is already growing research into the use of light and light-related products to help us to sleep better. As public awareness of this issue grows it is inevitable that interest in to this topic will increase. Perhaps such products could be used to mitigate the effects of poor sleep in situations such as the one I was in last week.
I noticed a story today about a bull that escaped during a rugby game in France. Why would a bull even be there? I have no idea. But what interested me was the trope that was repeated in the article about the concern that one of the teams was wearing red shirts and that this could put those players in particular danger.
As you may know, bull fighters use a red cape during bull fighting events and this is popularly believed to be to enrage the bull.
However, it turns out that bulls are dichromats. They only have two types of cones – the light-sensitive cells in our eyes – and they are missing the long-wavelength cones. This makes them colour blind and red-green colour blind in particular.
It isn’t the case that bulls are enraged by red; it is the movement of the cape that irritates them. It is my understanding that the red colour is used so that the cape doesn’t show the blood. This was discussed in the first of my podcasts – do dogs see colour – which you can listen to here.
Earlier today I posted something on quora about who many colours there are. It’s quite a long post. You can read it here. However, if you want the short cut the answer is 3-5 million. 🙂
However, I also linked to the post on LinkedIn and someone asked me a question about the relationship between colour-matching functions and cone sensitivities so I thought I would make a new post today about that topic. I have used my message on LinkedIn as the basis for this post but modified it a little to make it suitable for general consumption.
Here are two diagrams:
This shows the actual spectral sensitivities of the MLS cones in the human eyeThe 1931 CIE XYZ colour-matching functions
It’s another common misconception that people get these two diagrams confused. The cone spectral sensitivities are the actual sensitivities of the cones in the eye. Although people often say that the eye responds mainly to red, green and blue light, it’s not so simple. In 1931 the CIE measured the colour matching functions. One of the reasons that they did this was that in 1931 we didn’t actually know what the cone spectral sensitivities were; these were only known for sure in 1964. So in 1931 the CIE measured the amounts of three primary lights that an observer would mix together (additively) in order to match a single wavelength of light. And they did this for each wavelength. The second of the diagrams above shows the amounts of each of the primaries needed to match each wavelength on the spectrum. Originally, the CIE used three lights (these were RGB) or primaries. However, they mathematically transformed their RGB colour matching functions to create the XYZ colour matching functions. These are sometimes also known as the CIE colour matching functions or the CIE standard observer.
These are the original CIE RGB colour-matching functions
The point of these (XYZ) colour matching functions are that they allow us to calculate the CIE tristimulus values XYZ of an object if we know the spectral reflectance of the object and the light it is viewed in. The XYZ values are the amounts of the three XYZ primaries that an observer would, on average, use to match that object viewed in that light source. If two samples have the same XYZ values then they are a visual match; because an observer would, on average, use the same amounts of the XYZ primaries to match each. And this was the whole point of the CIE system; to determine when two colour stimuli are a visual match. Had we known the cone spectral sensitivities in 1931 it’s possible that history would have taken a different course and that instead of having CIE XYZ we would simply calculate the cone responses LMS. And we could say that if two samples have the same cone responses they are a visual match. But I guess we’ll never know.
Now, if two samples have the same XYZ values then they will have the same cone responses. This is a bit technical but this is true because the cone spectral sensitivities are a linear transform of the CIE XYZ colour matching functions. They are also a linear transform of the CIE RGB colour-matching functions.
The colour-matching functions depend upon which primaries are used whereas the cone spectral sensitivities are more fundamental. Doesn’t this make the colour-matching functions arbitrary? Not really. Although the actual shapes of the colour-matching functions depend upon the actual primaries used, the matching condition does not. If two samples generate the same cone responses then the observer would match them with the same amounts of the XYZ primaries and the same amounts of the RGB primaries.
I have been posting here on Colourchat for a long time. I think it is nearly 10 years but it could be longer. Time flies. However, I just wanted to let you know that I also post on a website called quora. Quora is a site where people post questions and other people can answer them. It used to be completely free although quora have recently introduced a model where people can put their answers behind a pay wall. However, my answers are free and I just wanted to let you know that there is a lot of stuff there that might interest you. I have only been posting there about 3 years but my answers have received over 2 million views (whereas Colourchat has had less then 500,000 views over a much longer time period).
However, quora is a little bit tongue-in-cheek. Not all of the answers are serious though most of mine are. I still reserve my best content for Colourchat where I can give a lot more detail. And I also have a patreon page where I do charge a small fee (because that’s how patreon works) where I am curating my most detailed content and this includes quite a few videos that are unique to the patreon site.
Anyway, if you want to have a look at quora you could take a look at this post I made today which answered the question of why a mixture of red and blue light doesn’t generate a hue that is between the two ends of the spectrum. I hope you like my answer. What I focus on – and what I am striving towards though perhaps not always achieving – is to try to answer these questions in a way that is maximally informative but at the same time doesn’t require an understanding of maths, for example, so that it is maximally inclusive.
On Dec 14th 2013 I posted about how the colour of your urine says something about your health (spoiler alert: the lighter it is the better!). Just over three years later I posted something similar, this time about the colour of poop. Let’s just say that you don’t want black.
Perhaps it is the time of year but today I read an article about why poop is brown. However, this time it was in TheConversation. TheConversation is an incredibly good website. It was first produced in Australia in 2011 and is a non-profit media outlet. In the UK it is supported the UK government and a number of UK universities (including University of Leeds where I work) to generate journalistic content that people can trust – academic rigour with journalistic flair.
I have only published in TheConversation once. I was invited to write about the effect of light on colour. I am quite proud of the fact that my article is the fifth most read article of any produced from the University of Leeds. It has 190,225 reads which is approximately 190,220 more reads than most of my academic papers ever achieve. So it’s a great way to get stuff out and have an impact.
However, I was invited to submit the article and even then I went through quite a rigorous process where the editor who is assigned to your case asks for evidence for every claim you make. So it’s not easy to publish there. The upshot of all of this is that TheConversation can be trusted. One of the problems with the current world, imho, is that the freedom that the internet has given us – where anyone can put stuff out there and where the world is no longer controlled by a small number of publishers – needs to be balanced by the problem that anyone can put stuff out there. There is more nonsense written on the internet about colour than almost any other topic apart from, perhaps, COVID, vaccines and masks. I won’t comment about those topics because I know no more about them than you – possibly less. But if you want to read reliable information about anything, written in a clear and simple way by people who study that topic for a living, I cannot recommend TheConversation more highly.
However, back to the more important topic – colour of poop. The article is actually a response to a question that was received from a child in Maryland and is part of a series for children of all ages called Curious Kids.
The brown colour is produced by the bile pigment stercobilin – first isolated from faeces in 1932 – without which poop would probably be very pale, almost white. The presence of this particular pigment in water is sometimes used to detect faecal pollution levels in rivers. So now you know one more colorant; albeit a natural one.
There is a related article about poop and health on TheConversation if you are interested. To make the point about articles in TheConversation being written by people who know what they are writing about they note in their article:
Have you ever wondered what’s going on in your poop? Perhaps not. But this is precisely what we think about every day at the American Gut Project, the world’s largest microbiome citizen science effort, located at UC San Diego School of Medicine.
