"When the Romans took over the Phoenician salt fish trade, they discovered how to make their purple dye. A logical by-product of fish salting, the dye was produced by salting murex, a Mediterranean mollusk whose three inch shell resembles a dainty whelk.According to legend, the presence of this dye was discovered when Hercules took his sheepdog for a walk along the beach in Tyre. When the inquisitive dog bit into a shellfish, his mouth turned a strange dark color. From at least as early as 1500 bc, this dye brought wealth to merchants in Tyre.
The painstakingly extracted purple dye was a luxury item of such prestige that the color purple became a way of showing wealth and power."
- from Salt by Mark Kurlansky
And who knew Hercules had a sheep dog? Very cute choice, Hercules.