They also produced the color purple or lavender from the murex mollusks that were found on the seacoast. Dye makers rubbed two of the mollusks together in order to extract the dye.

That sounds simple enough, but it also involved some real chemistry:

https://hal.science/hal-03202592/document

Purple was one of the most expensive and difficult dyes to acquire and process. 1 gram takes 10,000 snails. In Europe, it was solely used for kings.