Tag Archives: purple

Cadbury lose purple case


I have written a few times about various legal cases that are on-going to settle disputes about colour ownerships. For example, about 18 months ago I wrote about trademarking colour and the dispute between Cadbury and its competitors over the use of the colour purple (specifically Pantone 2685C) on chocolate packaging and advertising. In that blog I noted that Cadbury had lost a case in the USA against Darrell Lea but had been granted protection in the UK despite protests from Nestlé. The law is a complex matter.

However, today, in the BBC I read that Nestlé has won a court battle with Cadbury, over Cadbury’s attempt to trademark the purple colour of its Dairy Milk bars. This is a successful appeal by Nestlé to the earlier ruling. The Court of Appeal said that Cadbury’s trademark application lacked “the required clarity, precision, self-containment, durability and objectivity to qualify for registration”.

“We are disappointed by this latest decision but it’s important to point out that it does not affect our long held right to protect our distinctive colour purple from others seeking to pass off their products as Cadbury chocolate,” said a Cadbury spokesman. Watch this space!!

why are leaves green?

Why are leaves green? The most obvious answer is that they contain green pigments, the most abundant being chlorophyll and that chlorophyll absorbs the short and long wavelengths in the visible spectrum leaving the middle wavelengths to be reflected and scattered. However, the deeper question is why should chlorophyll absorb in the short and long wavelengths of the visible spectrum when there is more light available in the middle of the spectrum?

The spectral irradiance of sunlight varies with the time of day, the weather conditions, the time of year, and the latitude/longitude. However, I think it would be reasonable to say that by and large, in most situations, the peak irradiance is in the middle of the spectrum (that which we would normally associate with being green and yellow).

So if one assumes that evolution has produced a perfect engineering solution to this aspect of nature in particular then I think one may expect plants to absorb mainly in the middle part of the spectrum (and this would result in the bluish and reddish wavelengths being reflected and a purplish colour).

So why don’t we have a chlorophyll equivalent that is purple? I have come across a number of arguments.

1. One could go further and say that if a plant wanted to be really efficient it would absorb all wavelengths of the visible spectrum and would therefore appear black. So black, rather than purple, would be the perfect engineering solution. Given that most plants are neither black nor purple then I think we can assume that evolution did not find the perfect engineering problem or that the problem is more complex than we think. For example, it could be that a plant that is black would absorb too much light and overheat. Or it could be that chlorophyll evolved from some earlier light-sensitive chemical and that genetic mutations could lead more easily to chlorophyll than to purple or black pigments.

2. Taking this point further, I have heard it suggested that most plants evolved from earlier plants that lived under water and that absorbed mainly short wavelengths of light (long wavelengths – red – cannot penetrate much more than 1 m of water). These earlier cousins of the modern plant would most likely have been brownish. Indeed, if one looks today ay plants in seawater, green plants are only seen on the surface or at very low depths. So the ancestor of chlorophyll could have been a brown pigment which mutated into green chlorophyll more easily than it could have mutated into a purple pigment.

3. I have also come across the ‘early purple earth’ hypothesis. This suggests that originally most plant life on land was indeed optimally purple and that chlorophyll absorbed to take advantage of those wavelengths that were not already being gobbled up by the dominant species. Subsequently, chlorophyll proved more successful than its purple companion.

4. It could be argued that optimally absorbing light (and being purple) is not the most important thing and that there are other aspects of the problem that are more important. Green chlorophyll could be the optimal solution to this more complex problem.

In short, the real answer is … I don’t know. I am not overwhelmingly convinced by any of the above arguments.

If you enjoyed this post you may like to look at my special christmas post on carrots and why they are orange.

the colour purple

Much was made in the media this week about the front bench of the labour party (UK) all wearing purple during the announcement of the budget. However, remarkable though it was, it is not a totally new phenomenon. On a number of occasions in 2009 and even 2008 leading figures in the government have been seen wearing purple.

In fact, even in December 2008 Zoe Williams was writing about this in the Guardian – http://www.guardian.co.uk/lifeandstyle/2008/dec/08/fashion-ties-purple-gordon-brown. Zoe points out that the latest trend for wearing purple by politicians was probably started by Michelle Obama who famously wore the colour in August 2008.

Perhaps the labour politicians believe that purple represesnts a third way, halfway between red and blue (the colours traditionally associated with the left and right of UK politics respectively). Or perhaps they feel that it gives the impression of power and establishes them as the rightful winners of the forthcoming election. Purple was the colour worn by emperors and senators of course. Whatever the rationale, it is surely not a coincidence.

Colour ownership?

Can you own a colour?

The answer is almost certainly not. However, the law on colour use in branding and marketing is complex and there have been several high profile cases of companies slugging it out over the use of colour. I have previously posted about the dispute between Google and Microsoft – http://colourware.wordpress.com/2010/01/25/four-colour-primaries/.

There are two other high profile cases I know of. One is the objection by Orange (a British Telecoms company) to the use of the colour orange by Easy Jet – http://tinyurl.com/y8la766. The other is the dispute between chocolate manufacturers over the use of the colour purple in chocolate wrappers – http://tinyurl.com/y9cgyum.


However, in a paper published in the open access colour journal – Colour: Design and Creativity – Paul Green-Armytage argues that the key to many of these disputes about colour ownership lies in the definitions of colour. See http://www.colour-journal.org/2009/4/6/index.htm to read Paul’s full article.

why is hue circular?

Everyone is familiar with the colour spectrum. If you pass white sunlight through a prism then it splits into the component wavelengths. The shorter wavelengths appear blue, the longer wavelengths appear red, and in between we have the familiar colours that I learned as school as Richard Of York Gave Battle In Vain, for the sequence red, orange, yellow, green, blue, indigo and violet, and that I have since understood is taught in the US as a person: Roy G Biv. I wonder if there are any other mnemonics that people know of? Of course, many people believe that Newton was in error when he identified 7 colours in the spectrum – he was probably influenced by Aristotle who wrote about there being 7 fundamental colours as there are 7 tones in the musical octave. I’ve posted about the indigo issue before – http://colourware.wordpress.com/2009/07/20/indigo-a-colour-of-the-rainbow/ – so won’t repeat that here.

Newton was probably the first person to create a hue circle (others, such as Forsius, created colour cicles but often included white and black in the circles). Newton created a true hue cirlce where he took the colour spectrum and wrapped it around, noticing that the two ends of the spectrum (where the reds become bluish and the blues become reddish) look rather similar.

Of course, there was a gap because the two ends of the spectrum did not quite match and thus Newton had to add in some purplish colours – these are hues that are never seen in the spectrum (and are sometimes called extra-spectral hues or non-spectral hues). The hues in the spectrum can be created by a single wavelength; however, the extra-spectral hues only occur when we see several wavelengths at the same time. For example, when we see short and long wavelengths together we can see purple.

In my lecture at the University of Leeds (www.leeds.ac.uk) this week someone asked “Why do the two ends of the spectrum look similar at all when the light is so different physically (at one end the waves are short and high energy and at the other they are long and low energy)?” Very very good question – if changes in wavelengths change the hue why should wavelengths that are so different look so similar?

So, why is hue circular? The answer is that it has very little to do with wavelengths and physics and more to do with human physiology. The human visual system captures light with three classes of cell (called cones) in the retinae of the eye. The signals from these cones are processed by the human visual system to create opponent signals (red-green and yellow-blue). This puts red and green opposite each other and yellow blue opposite each other and results in the perception of hue being circular. It also explains why some hues particularly contrast – sometimes called complementary colour harmony.