Monthly Archives: December 2009

Why are carrots orange?

Carrots are orange because they absorb certain wavelengths of light more efficiently than others. Beta-carotene is the main pigment and is mainly absorbs in the 400-500nm region of the visible spectrum with a peak absorption at about 450nm. Carotenoids are one of the most important groups of natural pigments.  They cause the yellow/orange colours of many fruit and vegetables. Though beta-carotene is most abundant in carrots it is also found in pumpkins, apricots and nectarines.  Dark green vegetables such as spinach and broccoli are another good source.  In these the orange colour is masked by the green colour of chlorophyll.  This can be seen in leaves; in autumn, when the leaves die, the chlorophyll breaks down, and the yellow/red colours of the more stable carotenoids can be seen.

However, the properties of beta-carotene are not what prompted me to make this blog. Last night I was watching the 4th in the series of Christmast Lectures by Prof Sue Hartley – the Royal Institution Christmas Lectures are a series of lectures given by a prominent scientist each year to an audience of children and broadcast on TV –

Prof Hartley’s lecture was about selective breeding and how humans had used this technique of thousands of years to make food safer and easier to eat. The section about wheat was particularly good.

However, she also talked about the colour of carrots and said that not all carrots are indeed orange at all. They come in many varieties including white and purple.

Prof Hartley said that it was the Dutch who selectively bred wild (white) and cultivated (purple) carrots to create the orange ones that we all know today. The orange was popular because it is the Netherland’s national colour and, at the time, the Dutch were fighting for independence. It was this story that has led me today – yes, Christmas Day – to make a virtiual visit to the British Carrot museum to research this story. You can follow my tracks at – Yes, such a place really does exist! 🙂

It turns out the story is not so clear as that told by Prof Hartley (though I am sure she is aware of this and was simply making it interesting to the children).   Certainfly the first cultivated carrots – in the Afghanistan region – were purple and orange carrots were cultivated in Northern Europe about 500 years ago. However, some scholars dispute the Dutch story about breeding orange carrots because orange was the national colour. Indeed, there is, apparently, a Byzantine manuscript from as long ago as 512AD that depicts orange carrots. So the mystery deepens and I have far better things to do on Christmas day than to research this further. Perhaps if any experts in carrot technology come across this page they can add an informative footnote?

dark alchohol makes you feel worse

A paper in the journal Alchoholism: Clinical and Experiment Research by researchers at Brown University reveals that the colour of alchoholic drinks really does affect how bad you feel the next morning. Darker drinks (such as whisky) contain more chemical by-products than do lighter ones (such as vodka). However, how you feel (in terms of hangover) does not necessary correlate with performance loss the next day. So you may feel better drinking vodka but you would be just as incapable of driving or using heavy machines etc than if you drank whisky – though the latter may make you feel worse.


pink stinks?

PinkStinks ( is a campaign and social enterprise that challenges the culture of pink which invades every aspect of girls’ lives. The campaign has been running for 18 months and activists argue that while a wide variety of boys’ toys are available, those for girls are often predominantly pink. They argue that body image obsession is starting younger and younger, and that the seeds are sown during the pink stage, as young girls are taught the boundaries within which they will grow up, as well as narrow and damaging messages about what it is to be a girl.

It’s interesting that the notion of pink for girls and blue for boys has not always been so. A recent article on the BBC web site claims that in 1918 the Ladies’ Home Journal included the statement: “There has been a great diversity of opinion on the subject, but the generally accepted rule is pink for the boy and blue for the girl. The reason is that pink being a more decided and stronger colour is more suitable for the boy, while blue, which is more delicate and dainty, is prettier for the girl.” For more see

a new colour?

Even those not particularly interested in colour are likely to have heard or read news stories recently about the remarkable colour vision of shrimps; the mantis shrimp has been discovered to effectively have 12 different classes of wavelength-sensitive detectors (whereas most of us have only three!). I have already posted about this story before – see – and moaned about how many of the reports say that human can only see three colours (which is not the same thing as having three classes of cone – as our light receptors are known – of course).

However, today I was listening to BBC Radio 5 and I heard the latest development of this story which is that the mantis shrimp has now been shown to be able to differentially detect light according to how it is polarised. For a nice descriptiopn of what this means in simle English I recommend the article on the National Georgraphic website – However, the ‘popular interest’ angle of the story that was reported on the radio today was that shrimps can see colours that we cannot see. This notion that there are colours out there that have never been seen by humans, and that shrimps can see them, is interestig. Radio 5 ran a poll inviting listeners to phone in with their least favourite colour – if we could choose to see this new colour that shrimps can see but had to throw one existing colour out to make room for it, which one would it be? I didn’t hear the end of this but the first candidate for colorimetric execution was mustard colour!

Of course, that shrimps can detect wavelengths that we cannot see and can detect different types of polarization is one thing; claiming they can then see colours that we cannot, is quite another thing. I won’t ram this point home here but would simply quote Issac Newton who famously said that, to speak properly, the rays are not coloured. However, the notion of a new colour reminded me of a novel that was written in 1939 by Brian O’Nolan called The Third Policeman.  This is a strange book but the plot incorporates a man who paints his bicycle a colour that nobody has even seen before and that, if seen, would cause the observer to go insane. Sadly, the book failed to find a publisher whilst the author was alive. It was finally published in 1967, one year after the author’s death.


One of my favourite movies – especially at Christmas – is It’s a Wonderful Life; a 1946 American movie directed by Frank Capra and starring James Stewart, a man who is financially ruined and is about to commit siucide on Christmas Eve until he is visited by a guardian angel.

Today I saw a new colorized version of the movie being advertised on DVD (or maybe Blu-Ray, whatever that is). It turns out that it is not the first colorized version of this movie. The first was introduced in 1986 and improved upon in 1989. The process of colorization is a difficult and time-consuming process; essentially an artist adds colour to each frame of the movie (obviously this is usually done digitally on a computer). There are two interesting properties of the world and of colour vision that makes the process a little easier than it might otherwise be.

Firstly, colour varies slowly over the scene so that it is not necessary to individually colour each pixel; the artist can define an area an add a single colour to that area with a single mouse click. The importance of luminance for detecting edges and defining form allows some error in this process with the knowledge that it probably wouldn’t be noticeable to most observers. However, in addition to spatial smoothness, there is also temporal smoothness. So, most adjacent frames are very similar. This allows the artist to colorize every, say, 10th frame, and use interpolation to do the rest.

The results of colorization are sometimes disappointing, especially for flesh tones. However, the process is improving all the time and I look forward to seeing the latest results.

blue santa

In an attempt to influence the way in which the public perceive police offers, a program in Logan County (Ohia, USA) will have officers knocking on the doors of the needy bearing gifts, accompanied (where possible) by an officer dressed in a blue santa suit. 

 The program is designed for families with at least one child at home and is focused mostly on food, toys and clothing for young children. For more information about the Blue Santa program, contact Joe McBride at the Logan County Sheriff’s Office at (970) 522-2578, Ext. 3507.

The Blue Santa Program has its origins in San Antonio (Texas, USA) and goes back to 1976. It became an official programme of SAPD in 1986 –

By coincidence next year’s IS&T Color Imaging Conference will be held in San Antonio. For further information see