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 http://colourware.wordpress.com/2009/10/31/how-many-colours-are-there/ – 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 – http://news.nationalgeographic.com/news/2008/05/080519-shrimp-colors.html. 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.