Colour turns up in different cultures in a multitude of ways. It has come to symbolise feelings and important events - white for mourning in China, black in Britain. Red for love, danger and anger; white with rage - or white for a bride, although this tradition dates only from Victorian England. Blue symbolises cold and sadness, yellow stands for cowardice, green for envy and, like it or not, pink for a girl and blue for a boy.
Such symbols can arouse deep passions. From national flags to cardinals' robes, colour can also be used to express nationalistic or religious sentiments.
The human quest for colour spans many thousands of years, and it has always been big business. Its story brings together art, science, alchemy and magic; agriculture, mining, textiles and food; symbolism, religion and national or political identity; and it reveals tales of wealth, power and even empires.
Evidence from around the world shows that, in the earliest uses of colour, pigments were dug from the earth and transported, often large distances, to be used as paint. Images using these pigments have been found on the walls of caves, where ancient peoples imprinted their hands in red ochre, or painted a record of their dreams and stories and of the animals and objects that were important features of their lives.
These ancient artists relied on the earth around them - clays containing aluminium, iron, magnesium and potassium, and oxides of iron and manganese, which offered reds, greens, browns and yellows. Charcoal or charred wood or bone was used for black, and chalk or calcite for white. Pigments were made by grinding the ore and mixing the powder with animal fat, water or the artist's own spit to bind the colour to the rock surface. The oldest known mine in the world is in Swaziland, at Bomvu Ridge (bomvu means red in Zulu). The iron-rich haematite (red ochre) was dug from the ground there more than 40,000 years ago, together with a crystalline form of the ore, the shiny black specularite, which could only be obtained by deep excavation. These substances are still in use among the Swazi people as body paint.
As technological know-how developed, so did the range of colours available.
Many that are still in use today have fascinating histories. Take blues and purples. A strong blue was long sought after; the ancient Egyptians were very keen on it - the golden mask of Tutankhamun, who died around 1325bc, was decorated with blue glass strips. They also introduced new pigments, including azurite blue, and manufactured the first synthetic pigment, known as Egyptian blue, by grinding a copper-rich glass.
Ultramarine, much valued by artists through the centuries, is made from lapis lazuli and was first used as a pigment in Afghanistan in the 6th century. Ninth-century illuminated manuscripts were painted with blue inks derived from indigo and lapis lazuli.
Around the ancient Mediterranean world, trading in purple symbolised the making of empires. The Phoenicians reached the height of their power around 800bc. Their name comes from an ancient Greek word for Canaan, meaning land of purple, and they grew rich on harvesting a murex sea snail from which they produced Tyrian purple. Tyre was noted in its day for the stench from the dye works -thousands of the shells were required to make an ounce of this enormously expensive dye.
The colour is due to the presence of bromine, which the animal extracts from the sea and combines with indigo. On exposure to air, a complex reaction takes place and the pale solution (of dibromoindigo) becomes an intense purple. Hills consisting entirely of murex shells can be found on the Mediterranean coastline near Phoenician ruins.
This became the royal purple of the Romans. It took about 10,000 shells to produce a toga, so the cost was enormous. The Caesars went for the colour in a big way, decreeing that only the emperor was allowed to wear it. There was a ban on its use by Jews, whose prayer shawls contained a sacred blue thread produced by a secret process which vanished under Roman rule - until recently, that is, when Ari Greenspan, an enthusiast for such archaeological detail, went diving off the coast of Israel to find murex shells.
During his search, Greenspan discovered that the Arabic word for the snail is "chilzun", almost identical to the ancient Aramaic "chilazon". Back in the laboratory, the chemical secret was revealed when the presence of sunlight at a crucial stage created a bright indigo blue instead of the purple of the Caesars.
What is indigo? The name is derived from an old Spanish word for India - and the substance has been in fashion from the time ancient people discovered how to dye fibres. Obtained from plants, indigo's value as a dye gave it a pivotal role in many economies. In ancient Europe, the woad plant was the main source -the Picts of northern Scotland were so named by the Romans because of their use of woad indigo as body paint or tattoos. And because manufacture of the dye produces a terrible stench, Queen Elizabeth I decreed that no dyers could work with woad within five miles of a royal palace.
In the 1500s, England, France and Germany banned the importation of dye made from the indigo plant in India, although it was a stronger colour than woad indigo, because of the threat it posed to woad farmers. Dyers had to swear on oath that they would not use the indigo plant, on pain of death.
The ban lasted for hundreds of years, until the 18th century, when Portuguese and Dutch merchants imported indigo from India for use in the rapidly expanding textile industry, and European woad farmers were forced out of business. Meanwhile, purple went on to become the first of a new family of dyes - indeed, it signalled the start of the modern chemical dye-manufacturing industry based on organic chemicals (compounds containing carbon atoms).
In 1856, a purple dye was created accidentally, by William Perkin, a teenage chemist who was trying to synthesise quinine. He realised that his mistake might lead to an important discovery and instead of binning the splodge of purple he went on to market the new dye as "mauveine". Queen Victoria loved it, ordering silk gowns in mauveine and declaring it the "colour of the decade". Mauveine was the first of many dyes derived from aniline (from anil, the Spanish word for indigo). William Perkin went on to become rich and successful.
In the 19th century, the British forced many Indian farmers to abandon subsistence farming for cash crops, and large tracts of land were planted with indigo. This resulted in high food prices for the peasants, while the commercial benefits went to the British. In 1859-60 there was a farmers' revolt, known as the "blue rebellion" or the "indigo war". But the system continued until 1917, when Gandhi's support for the indigo farmers led to his trial for civil disobedience, and a committee of inquiry subsequently recommended an end to the compulsory growing of indigo.
Since indigo was a strong, colourfast dye, by the end of the 19th century, 400,000 tons a year was being produced, much of it for military uniforms in Germany, France and Britain. But the hugely successful German chemical industry then mounted a challenge to Britain's monopoly of the European market, with a much cheaper synthesised indigo, although the British government continued to use only the natural dye for its Navy blue. In 1918, the Allies acquired German patents for synthetic dyes as part of the price paid by Germany for losing the war. Indigo farming in India and the West Indies came to an end, and the US and UK developed modern chemical dye-production.
Insects have also often been the key to colour. Carmine and cochineal were both made from the dried bodies of insects. Kermes vermilio is native to Europe and the Mediterranean and lives on the Kermes oak. Cochineal, which is in widespread use today as a food dye, comes from a similar insect, Dactylopius coccus, which feeds on the prickly pear cactus and is found throughout Central America and Mexico. Cochineal red was made by the Aztecs and brought to Europe in the 16th century by the Spanish conquistadors, soon replacing the kermes-derived carmine because of its stronger colour.
The name is derived from an Aztec word meaning "blood of the prickly pear".
Today, whole areas of Peru, Mexico and the Canary Islands are dedicated to growing the prickly pear in order to harvest the insects, providing the bright cochineal red in many soft drinks, cakes, biscuits and sweets, and even in aperitifs such as Campari. And "beetle" red, an edible dye in use for thousands of years in different parts of the world, takes us from palette to palate. Because, although we may not be aware of it, countless decisions we make every day involve colour, and often in a subconscious way.
This is where the marketing and packaging gurus come into their own, relying on colour to get us to buy their clothes, drive their cars and, above all, eat their food. Food-marketing experts will say in no uncertain terms that unless they get the colour right, we won't buy their products.
We may be happy to leave it to the regulators to ensure that the colourings used are safe to eat, but we tend not to delve too deeply into how the regulations are made, or how the food is tested. We continue to buy dyed food, even when faced with lists of ingredients that sound quite alarming.
One company, with expertise in inks for inkjet printers, as well as dyes for the food industry, is even developing edible inks that can be printed directly on to food. They seem to think this will be a profitable move.
Red is an important colour in choosing food, especially many types of fruit, which we select initially by the shade of red on display. That's why stall-holders like to turn paler peaches red-side up. For fruit-growers, timing is crucial - pick it too soon and it won't ripen; pick it too late, and it could be rotten before it reaches your fruit bowl. If you've wondered why in recent times those deliciously ripe-looking red peaches remain rock hard for days on end, it could be that the fruit was sprayed before harvesting with a substance known as LPE (lysophosphatidylethanolamine). LPE is derived from soya and egg yolk and has been found to accelerate the reddening process in some fruits.
Originally developed for the cranberry farmers in Wisconsin, where the climate prevented their crop from acquiring the deep red that tempts us to buy it, LPE was discovered to have the added benefit of extending the ageing process, and hence the shelf life of the product. And, as it can be claimed that soya and eggs are of organic origin, this chemical is also used to spray organic fruit.
Sometimes, colour is added to the food before it is produced - a dye known as canthaxanthin is put into chicken feed to deepen the yellow of egg yolks. It is also used by fish farmers to enhance the pink colour of salmon, in spite of human health concerns. One chemical company has even produced a colour chart which enables farmers to choose the exact pink they want for their fish, or yellow for their egg yolks.
But enhancing the colour of manufactured food is nothing new - it goes back thousands of years, and does not always sound appetising. The ancient Romans and Greeks appointed inspectors to oversee the artificial colouring of wine. In the 1800s, in England and the US, a partiality for pickles could lead to a painful death, as these were often made bright green by the addition of a poisonous copper-based dye.
These days, we need to look not just at the intent of the perpetrators of such adulterations, but at our own motivations when we choose what to eat.
Isn't it enough that there are pesticides, fertilisers and genetically-modified crops to worry about, without potentially hazardous chemicals adding colour?
With modern consumers demanding natural and organic materials, new products are coming on to the market. Forward-looking chemical companies are producing organic paints, especially desirable in view of the toxic fumes that can be given off by many commercial paint products. And in 1991, an EU-funded project was launched to develop sustainable ways to grow indigo-producing plants in European countries, including woad and Japanese indigo (Polygonum tinctorium). So next time you buy a pair of blue jeans, look out for brands with natural indigo.
In the ancient worlds of China, India, Babylon, Greece, Egypt and Rome, saffron was a highly valued cooking ingredient, used for colour as well as for adding a distinctive flavour. It was also very expensive, consisting of the dried stigmas of a variety of crocus - more than 50,000 stigmas are required to produce 100g of red saffron, and each has to be picked by hand.
Around 1000bc, the Phoenicians traded saffron around the Mediterranean and beyond. Used as a dye for textiles and food, it reached England as part of the Phoenician trade with tin miners in Cornwall. In the Middle Ages, it was produced in Essex, around Saffron Walden.
In Greece and Rome, it was used to perfume the bath and as a medicine. In Germany in the 15th century, adulteration of saffron was a capital offence.
In Kashmir, saffron has been grown for thousands of years and is still an important cash crop today. Now opium growers in Afghanistan are being persuaded to switch to saffron production, in the hope of cutting the opium trade.
* Colour: Making and Using Dyes and Pigments by Francois Delamare and Bernard Guineau (Thames and Hudson New Horizons series, pound;6.95).
* Bright Earth: The Invention of Colour by Philip Ball (Penguin Pounds 9.99).
* Colour: Travels Through the Paintbox by Victoria Finlay (Sceptre pound;9.99) Links
* Webexhibits, a US online museum webexhibits.org
* The Society of Dyers and Colourists has an interactive museum of colour www.sdc.org.ukmuseummus.htm
* Interactive site exploring many aspects of colour www.colormatters.com
* Ari Greenspan's description of sacred indigo is published in It's Elemental:The Periodic Table, a special edition of the online magazine of American Chemical Society. There are also fascinating contributions for the other elements.
Our normal perception of blue in relation to food is that the food is off.
Indeed, blue is seen by food-psychologists as a colour that reduces appetite. However, in 1995, Americans were invited to vote for a new colour for MMs sugar-coated chocolates. Blue won by a landslide, with 54 per cent of more than 10 million votes cast.
A few months ago, a new food scandal hit the headlines - a "killer colour", Sudan 1, had slipped the net of EU regulations and contaminated many leading brands of processed foods. Few of us had any idea what it was, or why it was there, but we carefully examined the published lists of hundreds of products to make sure the poisonous stuff wasn't lurking in a kitchen cupboard.
Sudan 1 is one of a group of synthetic red dyes, normally added to polish and petrol, which are known to be carcinogenic. Also known as CI Solvent Yellow 14, it is part of a large group of "azo" dyes and has the chemical formula 1-phenylazo-2-naphthalenol.
Sudan 1 had been used for colouring various foodstuffs, but is now banned in many countries. This particular story had its origins in India, where the dye was added to a batch of chilli powder exported to Europe in 2003.
It seems that the consignment arrived before the EU brought in regular testing for "sudan" dyes, and so it slipped through unnoticed.
Spices - and colours - have always been traded over huge distances, but the Sudan 1 affair has highlighted the extent to which globalisation can affect what appears to be a fairly mundane shopping basket. Consumers of all social classes around the world were affected, shopping for anything from palm oil and curry powder to vegetarian ready meals and liver and bacon hotpot.