πορφυρίζω
From LSJ
ἵνα οὖν μηδ' ἐν τούτῳ δῷ αὐτοῖς λαβήν (Photius, Fragments on the Epistle to the Romans 483.26) → so that he doesn't give them even here a handle (= an opportunity for refutation)
English (LSJ)
A to be purplish, Dsc.3.36, Apollod.Ath. ap. Ath.7.281f; of the sea, Arist. Mir.843a26:—Med., Apollon.Lex.s.v. πορφύρῃ.