Twilight: Why Do The Cullens' Eyes Change Color?
The world of Stephenie Meyer's "Twilight" has always played fast and loose with modern sensibilities about vampire mythology. In the town of Forks, Washington, there will be no fangs or coffins. Instead, these sparkly vampires never sleep and secrete special venom that turns humans into one of them. These rules more resemble the archaic lore surrounding fairies than those of vampires, but it is Meyer's world, and we are all just living in it.
Older fans will notice that in "Twilight," the Cullen clan lacks the moral ambiguity that gothic vampire writers like Anne Rice expertly weave into their stories. Instead, Meyer has created heroic vampires that are so in line with morality that even their eye color is different from other vampires. No more messing around with fascinating characters who have different and nuanced ideas about possessing the dark gift; instead, "Twilight" makes it clear who is good and who is bad. All you have to do is look at the color of their eyes — so why do their eyes sometimes change color?
It's all about a healthy diet of blood
Carlisle Cullen's (Peter Facinelli) family of morally superior vampires holds themselves to a higher standard than those around them. Though the predatory species is specifically designed to allure humans, the doctor has trained his family to only prey on animals. This is how Edward (Robert Pattinson) and the rest of the coven get their golden eyes.
Other vampires, such as the sadistic Jane (Dakota Fanning), have blood-red eyes from feasting on humans. When Bella (Kristen Stewart) first turns into a vampire, she also sports this bloodthirsty look because her body is still full of human blood so soon after her transformation. Though Rosalie (Nikki Reed) has canonically never tasted human blood, her eyes are red in her vicious flashback sequence because she was a newly turned vampire. It takes months of an animal blood diet for newborn vampires' eyes to lose their ruby-hued color.
And then there is the third option that all vampires theoretically get: the look of starvation. Vampires don't necessarily starve like humans do, but they need a steady diet of blood to keep their strength up. At certain points, when the Cullens aren't fully satiated, their eyes turn a disturbing black color, as Bella notices when she first encounters Edward. After he goes on a hunting trip, his eyes turn from black to gold, illustrating that as long as the Cullens are fully sated without feeding on humans, their eyes will continue to have a golden hue.