I'm sticking with the theory of Lily having been adopted. Or perhaps the Dursleys really are related to Slytherin. J.K.R said we would learn something about the Dursleys too.
Far out theory, but perhaps Petunia is a squib?
Like someone had already said, how do people become wizards if they are muggle borns? Just wondering...
I don't think Lily was adopted, I just think she was like a regular muggle born and got married to James and was a sister to Petunia and that's how Harry was related to good ol' Petuny.
For some reason, I really don't want something major about the eyes, even though I know JKR said that... It just seems... Weird, I guess? A major secret about the -eyes- of Lily/Harry...
I agree with Barny The Barn about their idea of Slughorn. =D
And I think green is just a random color JKR picked...