What best explains the metaphorical meaning of blue skin in the poem Masks by Shel Silverstein

But this, but you – small, pitiful and twiggy – you put me down with wine, you blinded me. come back, odysseus, and i'll treat you well, praying the god of earthquake to befriend you – his son i am, for he by his avowal fathered me, and, if he will, he may heal me of this black wound – he and no other of all the happy gods or mortal men.' few words i shouted in reply to him: 'if i could take your life i would and take your time away, and hurl you down to hell! the god of earthquake could not heal you there! ' at this he stretched his hands out in his darkness toward the sky of stars, and prayed poseidon: 'o hear me, lord, blue girdler of the islands, if i am thine indeed, and thou art father: grant that odysseus, raider of cities, never see his home -the odyssey, homer what motivates cyclops to ask poseidon to interfere with odysseus's journey home?