Actually I have noticed this, And I thought I was going to far when I thought of this, but, I think eye color has something to with how powerful you are, or how much power is possible rather, because if you think of it Voldermort color that is always showing is green,9remember the mark) and he is one of the most powerful in the world, but my theory might totally be off base, I don't know what color Dumbledore eyes are do you know? Well no matter that I don't think Dumbledore is as powerful as Voldermort, but rather geniuses like Hermione. Which is why Dumbledore has not done away with Voldermort by now, he knows that. I might be a bit off base thou what do you think