Purple

Purple, the name and the colour, comes from a dye made from the mucus glands of a tropical sea snail, the murex (porphyra in Greek, purpura in Latin).

This discovery is attributed to the Phoenician god Heracles, the guardian deity of the city of Tyre.

One day his dog bit into a murex shell and its mouth immediately turned purple.

His companion, the beautiful nymph Tyrus, declared she would sleep with the god only if he dyed her a garment in the same shade.

Heracles obliged and the famous Tyrian purple dye was born.
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Purple land
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The dye, and the cloth made from it, was so famous that the Greeks called the land of Tyre and Sidon (equivalent to modern Lebanon) Phoinike, "the land of the purple".
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It required 250,000 shellfish to produce one ounce of Tyrian purple dye, making it very slow and costly to produce.
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The preferred method was to collect vast piles of shellfish and to allow them to decompose in the sun (classical authors attest to the stench).
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Production and export of the dye began around 1,200BC and fuelled the Phoenician expansion across the Mediterranean.
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By the third century BC, Tyrian purple was worth more than gold: a pound of it cost three times the yearly wage of a Roman baker.
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Purple royal
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Although the Greeks were the original customers, it was the Romans who became purple fanatics.
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They liked a dark shade, achieved by using dyes from two species of murex, one a dark indigo.
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Pliny the Elder described it as the "colour of clotted blood" and wrote that "it brightens every garment, and shares with gold the glory of the triumph".
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Triumphant generals wore robes of purple and gold while senators and consuls wore bands of purple at the edges of their togas.
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In imperial Rome, the use of purple was even more highly regulated: by the fourth century AD, only the emperor was allowed to wear the best purple.
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The colour's exclusivity and connection with power is why royal robes and the vestments of bishops have traditionally been purple.
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Purple peas
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The centuries-old recipe for Tyrian purple was lost to the Western world in 1453, when the Ottoman Empire conquered Constantinople.
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It wasn't until 1856 that the secret of purple was rediscovered, when Félix Henri de Lacaze-Duthiers, a French zoologist, saw a fisherman squirting a design on to his shirt using a shellfish.
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In 1909, the Austrian chemist Paul Friedländer worked out the chemical properties of the dye and saw that it was almost the same as blue indigo, extracted from an Indian pea plant called Indigofera tinctoria.
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Indigo is also present in Isatis tinctoria, a member of the cabbage family – better known as woad.
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Woad, a popular dye for the Celts and Vikings, is now being used in ink cartridges for printers, because it is more environment-friendly than synthetic blue dyes.
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Purple Earth
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In 2007, a team of geneticists at the University of Maryland suggested that early life on Earth might have been purple.
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Whereas plants now use chlorophyll to harness the sun's rays, ancient microbes used retinal (a form of vitamin A) to photosynthesise.
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Retinal is a simpler molecule and easier to produce in a low-oxygen environment such as that of early Earth.
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It absorbs green light and reflects back red and violet, which would make the microbes appear purple.
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The team believes microbes using chlorophyll evolved to absorb those red and blue wavelengths that retinal did not use.
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In the end, the more efficient chlorophyll-using microbes prevailed (which is why plants are green, not purple).
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Purple frog
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In 2003, a very odd species of frog was found in the Ghat hills in India. Nasikabatrachus sahyadrensis (which means "nose frog from Sahyadra") is a 3in-long dark purple, shapeless blob with a pointy snout.
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It spends its time buried underground feasting on termites, surfacing for only two weeks a year to mate.
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The males make a loud noise like a chicken.
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The purple frog is unique: its closest relatives live on the Seychelles, but it split from them more than 130 million years ago.
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Molly Oldfied - John Mitchinson