Of Latin origin; the "purple" mussel, i.e. (by implication) the red-blue color itself, and finally a garment dyed with it -- purple.
Thayer's Greek Lexicon
Strong's 4209: πορφύρα
πορφύρα, πορφύρας, ἡ, the Sept. for אַרְגָמָן;
1.the purple-fish, a species of shell-fish or mussel: (Aeschylus, Sophocles), Isocrates, Aristotle, others; add 1 Macc. 4:23, on which see Grimm; (cf. B. D., under the word 1).
Mark 15:17 - N-AFS GRK:ἐνδιδύσκουσιν αὐτὸν πορφύραν καὶ περιτιθέασιν NAS: They dressed Him up in purple, and after twisting KJV: him with purple, and INT: they put on him purple [garment] and placed on
Mark 15:20 - N-AFS GRK:αὐτὸν τὴν πορφύραν καὶ ἐνέδυσαν NAS: Him, they took the purple robe off KJV: they took off the purple from him, INT: him the purple [garment] and put on
Luke 16:19 - N-AFS GRK:καὶ ἐνεδιδύσκετο πορφύραν καὶ βύσσον NAS: and he habitually dressed in purple and fine linen, KJV: was clothed in purple and INT: and he was clothed in purple and fine linen
Revelation 18:12 - N-GFS GRK:βυσσίνου καὶ πορφύρας καὶ σιρικοῦ NAS: and fine linen and purple and silk KJV: fine linen, and purple, and silk, INT: of fine linen and of purple and of silk