The dye was very hard to make in ancient times,so only the wealthy could afford it:
"History, Shellfish, Royalty, and the Color Purple
Jul 1, 2002 12:00 PM, Dr. Richard M. Podhajny, Ph.D. Contributing Editor
Understanding color is one of the keys to success in the printing industry. It also can be very interesting history.
A dictionary defines purple as “any of a group of colors with a hue between that of violet and red” and as a “symbol of royalty or high office.” Historically, the color purple has been associated with royalty and power, but the secret of its power lies in the glands of tiny shellfish creatures.
The earliest archaeological evidence for the origins of purple dyes points to the Minoan civilization in Crete, about 1900 B.C. The ancient land of Canaan (its corresponding Greek name was Phoenicia, which means “land of the purple”) was the center of the ancient purple dye industry.
“Tyrian Purple,” the purple dye of the ancients mentioned in texts dating back to about 1600 B.C., was produced from the mucus of the hypobranchial gland of various species of marine mollusks, notably Murex. It took some 12,000 shellfish to extract 1.5 grams of the pure dye. Legend credits its discovery to Herakles, or rather to his dog, whose mouth was stained purple from chewing on snails along the Levantine coast. King Phoenix received a purple-dyed robe from Herakles and decreed the rulers of Phoenicia should wear this color as a royal symbol.
Although originating in Tyre (hence the name), man's first dye chemical industry spread throughout the world.
Rome, Egypt, and Persia all used purple as the imperial standard. Purple dyes were rare and expensive; only the rich had access to them. The purple colorants used came from different sources, most from the dye extraction from fish or insects.
The imperial purple of Rome was based on mollusk from which purpura comes. Emperor Aurelian refused to let his wife buy a purpura-dyed silk garment, as it cost its weight in gold!
Insect and snail animal-based colors were mentioned in the Bible for use in textile furnishings of the Tabernacle and for the sacred vestments for the High Priest Aaron, and they also were used in King Solomon's and King Herod's temples in Jerusalem.
With the decline of the Roman Empire, the use of “Tyrian Purple” also declined, and large-scale production ceased with the fall of Constantinople in 1453 A.D. It was replaced by cheaper dyes such as lichen purple and madder.
Pope Paul II in 1464 introduced the so-called “Cardinal's Purple,” which was really scarlet extracted from the Kermes insect. This became the first luxury dye of the Middle Ages.
Dyes were exported extensively from Central and South America during Spain's exploration of North and South America. Among these were Cochineal from Mexico and Peru.
The chemical birth of the synthetic dye industry can be traced to the discovery of an aniline-based purple dye, mauveine, by William H. Perkin in 1856, who accomplished this while searching for a cure for malaria. Perkin was an English chemist who changed the world of his time by making this purple color available to the masses. It became quite fashionable to wear clothing dyed with “mauve,” and Mr. Perkin became a very wealthy man.
In 1909 Paul Friedlander determined the major chemical composition of Murex dye as 6,6'-dibromoindigo.
Today, genuine “Tyrian Purple” remains the domain of the rich and famous. However, synthetic dyes and pigments that meet various purple color requirements have removed the mystique of the color purple."