Augustine of Hippo
Catena Aurea · Matthäusevangelium 27
Then the soldiers of the governor took Jesus into the common hall, and gathered unto him the whole band of soldiers. And they stripped him, and put on him a scarlet robe. And when they had platted a crown of thorns, they put it upon his head, and a reed in his right hand: and they bowed the knee before him, and mocked him, saying, Hail, king of the Jews! And they spit upon him, and took the reed, and smote him on the head.
(ubi sup.) Hence we understand what Mark means by clothed him with purple; (Mark 15:17.) instead of the royal purple, this scarlet cloak was used in mockery; and there is a shade of purple which is very like scarlet. Or it may be, that Mark spoke of the purple which the cloak contained, though its colour was scarlet.