Purple was rare and hard to process…

… coming in ancient times from murex, a molllusk which yielded “purpurea”.  Purple was in high demand by emperors like Rome’s.  No one else could afford it: 1 lb of cloth dyed with murex in the time of the ancient Romans was worth $20,000 today.

(image: Etruscan fresco showing high ranking people wearing purple dyed silk)