Purple
Purple has long been associated with royalty, originally because Tyrian purple dye was extremely expensive in antiquity.[7] Purple was the color worn by Roman magistrates; it became the imperial color worn by the rulers of the Byzantine Empire and the Holy Roman Empire, and later by Roman Catholic bishops. Similarly in Japan, the color is traditionally associated with the emperor and aristocracy.[8]
Mythology
Julius Pollux, a Greek grammarian who lived in the second century AD, attributed the discovery of purple to the Phoenician god and guardian of the city of Tyre, Heracles.[63] According to his account, while walking along the shore with the nymph Tyrus, the god's dog bit into a murex shell, causing his mouth to turn purple. The nymph subsequently requested that Heracles create a garment for her of that same color, with Heracles obliging her demands giving birth to Tyrian purple.
Heracles was a divine hero in Greek mythology, the son of Zeus and Alcmene, foster son of Amphitryon.[3] He was a great-grandson and half-brother (as they are both sired by the god Zeus) of Perseus. He was the greatest of the Greek heroes, a paragon of masculinity, the ancestor of royal clans who claimed to be Heracleidae (Ἡρακλεῖδαι), and a champion of the Olympian order against chthonic monsters. In Rome and the modern West, he is known as Hercules, with whom the later Roman emperors, in particular Commodus and Maximian, often identified themselves.
https://en.wikipedia.org/wiki/Purple#Mythology