Creon is an elderly king of Corinth. It's his daughter that Jason, Medea's husband, wants to marry. Creon fears Medea, he knows she is not a woman to be messed with, and a sorceress to boot. He tries to banish her, but she convinces him to let her stay one more day. He gives in, and she ends up killing his daughter with a poison gown, which he too touches and dies from. I put him in black to portend the darkness which will soon befall him, and with the violet himation it gives him a very regal aire. He is trying to show his position of power, and thusly all the richly trimmed finery.