Lyric question - Emerald Eyes by Eric Johnson

In Eric Johnson’s song, Emerald Eyes, he sings:

Correct me if I’m wrong, but emeralds are green, and emerald eyes would be green eyes, right?

Does blue eyes imply an emotion state (such as “feeling blue”)? It’s weird that he says the eyes are blue when he’s talking about them being emerald eyes. I guess I’m missing the point of the emerald eyes/blue eyes thing… can you help please?