Vampires are meant to drink human blood. It is natural instinct, and most do it. The vampires that refrain from consuming humans and consume animal blood instead are the Cullens; they are the peaceful vampires. Vampires who normally drink human blood have red eyes, and get dull when they become thirsty. Unlike them, the Cullens' eyes grow a dark brown when they need more, and turn into a lighter, creamier golden once hunger is fulfilled. The Cullen family, however, has to feed more because animal blood doesn't satisfy their thirst as long as human blood would.

In the "Twilight Saga" mythos, vampires with red eyes indicate that the vampire has eaten human blood, which is why James' coven has red eyes as well as the Volturi.

If a vampire has only had animal blood ("vegetarianism" as the Cullens say), like Edward's family, their eyes would be golden.

A newly embraced vampire would have red eyes for a time even if he or she only eats animal blood after becoming a vampire because he or she has consumed human blood in order to make the change.

All vampires' eyes become black when hungry.