In case one was wondering if a Rishon was explicit in what Techeiles and the source is, to me the most blatant one is the Raavya (https://en.m.wikipedia.org/wiki/Eliezer_ben_Joel_HaLevi) to explain Brachos 1 Halacha 2 in the Talmud Yerushalmi . While more recent editions came out with it written “bein purfirin ubein prifinan,” prifinan being a gibberish word, the original manuscript reads “bein purfirin ubein prisinan,” which makes a lot more sense now. Both words are from Greek. Purfirin is that which is derived from the purfira/purpura, aka murex snail. Prasinan means leek green, and even today, Prasa is used in Greek and Greek ladino to refer to the leek vegetable.