Category Archives: knowledge

Extraordinary facts relating to the vision of colours

In 1794 John Dalton presented a lecture to the Manchester Literary and Philosophical Society about colour vision. The first two sentences are shown below:

It has been observed, that our ideas of colours, sounds, tastes, etc. excited by the same object may be very different in themselves, without our being aware of it; and that we may nevertheless converse intelligibly concerning such objects, as if we were certain the impressions made by them on our minds were exactly similar. All, indeed, that is required for this purpose, is, that the same object should uniformly make the same impression on each mind; and that objects that appear different to one should be equally so to others.

It is interesting to reread this sentence again in the light of the recent controversy about the blue and black dress.


colour and branding


According to Jon Feagain colour affects brand development in five ways:

    It helps boost perception

    It attracts attention

    It can help to emphasise or conceal information

    It can help you appeal to the right audience

    It can can help the audience digest information better

I think all of these things are true. However, to make the right decisions a good understanding of colour semiotics is critical in my opinion. Achieving that is easier said than done.

check your urine colour!


Just key urine colour chart into google images and prepare to be amazed. There are so many different charts and blogs and experts. Who would have thought it!! Today I saw an article in The Guardian that inspired to be to make this search. It turns out that there is a new urine colour chart from a clinic in USA that allows you to make a self diagnosis of your health based on the colour of your wee. A case of cross-media colour reproduction if ever I saw one (a poor joke that, for colour imaging scientists who may come across this blog).

I’m not sure it’s news though since there are a plethora of interesting charts for this already in existence and according to The Guardian the philosopher Theophilus noted the medical value in looking at the colour of urine as long ago as 700AD. However, if you have strangely coloured urine you might want to have a quick peek at The Guardian article to put your mind at rest (or not, as the case may be). Mine, for those who are interested, is sometimes clear but sometimes yellow verging on orange which is, I believe, because I don’t drink enough water. If you have blue urine it’s time to worry apparently.

why do we value gold?


Could we have developed currency around elements other than gold and silver? Why couldn’t we have coins made out of platinum, for example?

Interesting article today on the BBC website interviewing Professor Sella (University Collage London) about why, of the 118 elements of the periodic table, it is gold (alongside silver) that we value and use for currency.

According to Prof Sella there are reasons to dismiss all the elements apart from gold and silver. For example, you couldn’t use elements that are gas (such as neon) or liquid (mercury) as currency because it would be impractical to carry them around. Several others (such as arsenic and the other liquid, bromine) are poisonous and so could not be practically used. The alkaline metals (those on the left-hand side of the periodic table) are not stable enough (they react with too many other elements). And, of course, say no more about the radioactive elements. Some of the so-called rare earths (such as cerium) could be used but they tend to be even more rare that gold and are actually quite difficult to distinguish from each other.


Prof Sella also postulates reasons for dismissing the 40 transition and post-transition elements such as copper, lead, iron and aluminium. Many are hard to smelt (needing temperatures as high as 1000 deg C) such as titanium and zirconium or hard to extract such as aluminium. Iron is easier to extract and smelt but rusts too easily. Iron is also too abundant.

Prof Sella lists the 8 noble metals (platinum, palladium, rhodium, iridium, osmium and ruthenium, gold and silver) as contenders. However, with the exception of silver and gold they are too rare and have other problems (platinum is hard to extract and has a very high melting point for example). So this leaves gold and silver. The choice of these metals is not arbitrary. It turns out that they have exactly the right properties that we need. They are stable, chemically uninteresting, rare (but not too rare), safe, relatively easy to extract, solid at room temperature and with a reasonably low melting temperature.

The article also explains why gold is golden in colour.

I like my carrots black


On Christmas day of 2009 I posted about the colour of carrots.

I had been watching a Royal Institution Christmas Lecture by Prof Sue Hartley about carrots and why they are orange. She spoke about selective breeding by the Dutch (the first naturally occurring carrots were purple – from Afghanistan – and were later cultivated to be orange). In seeking to find more about this I found myself on the website of the British Carrot Museum. It is seriously worth a visit even if your interest in carrots is tangential.

I was reminded of this today when I came across an article in The Economic Times (India) which reported that the Punjab Agriculture University has developed its first black colour carrot variety (known as ‘punjab black beauty’) which has been recommended for general cultivation in the state. The black carrot is the best alternative to tackle the malnutrition problems of the country because it is overloaded with beneficial anti-oxidants and nutrients. The punjab black beauty is is rich in anthocyanins, phenols, flavonols ß-carotene, calcium, iron, and zinc.

I am also reminded, of course, of the words of the great late Uncle Monty (aka Richard Griffiths): “I think the carrot infinitely more fascinating than the geranium. The carrot has mystery. Flowers are essentially tarts. Prostitutes for the bees. There is a certain je ne sais quoi – oh, so very special – about a firm, young carrot”.

MRes Colour Communication

colour communication

We’re starting a new programme at Leeds University next September. It’s MRes Colour Communication. This is a one-year Masters programme by research but with a twist. There is a taught component in the first semester to get everyone up to speed to make sure they understand the basics of colour communication. They then explore one aspect of this in their research project and submit a dissertation at the end of the year. Please contact me at my University email of for further information or visit

dog vision

I just read an article in The Daily Mail that says that most people think dogs do not have colour vision. The article then goes on to say that Russian scientists have proved that dogs do have colour vision. It seems to me quite accepted that dogs are dichromats – that is they have two types of light-sensitive cells that contribute to colour vision in their eyes. We – humans – are trichromats because we have three such cells. It turns out that the one that is missing – in dogs – is such that dogs’ colour vision is rather like that of a human who has red-green colour blindness. The image below shows how the spectrum looks to a trichromatic human and a dichromatic dog.


As you can see, dogs can bee blues and yellow but have difficulty discriminating between colours in the red-green part of the spectrum. So I am not sure what the fuss is about with the Daily Mail article. After all, everything in the Daily Mail is true!! See if you don’t believe me.

eyes change colour?


I didn’t realise how sophisticated reindeers are. It turns out they have two layers of fur to help them keep warm, are able to shrink the pads on their hooves to give then better grip, and can detect ultraviolet light which enables them too see in very dim light. And it also turns out that their eyes can change colour in winter so that their vision is more sensitive. Reindeers, like cats, have a reflective layer behind the retina (which is the inside of the eye ball where all the light-sensitive cells are) that helps them to see in dim light. This is why, if you see a cat at night, you might see the eyes shining; you are seeing light being reflected back at you from the cat’s tapetum lucidum (which is the technical term for the layer behind the retina). The light that shines back in most animals with this layer is golden but in reindeer it apparently shifts to blue in the winter. The shift to blue allows more light to be scattered and improves the vision of the animal.

The full paper can be read in the Proceedings of the Royal Society.


As some of you may know, I was General Chair of AIC2013 this year. We had a great time in Newcastle and spent a week with over 600 delegates talking about colour. But time moves on and we are approaching 2014. I would therefore like to draw your attention to the next AIC meeting which is in Mexico in October 2014. The theme is colour and culture and the venue – Oaxaca – is stunning. I hope to see you there.

For further details visit