Why did Bella get red eyes?

A vampire’s eye color is indicative of their diet, namely regarding the intake of blood. In the case of the Cullen family, including male protagonist Edward Cullen, their eyes are yellow or honey-golden. This represents the fact that they feed only on the blood of animals and not humans. This yellowish color is a dilution of a vampire’s naturally ruddy eyes, which, along with the fact that it reflects a lack of human blood consumption, makes them looked down upon as abnormal in the vampire world.
Only Edward Cullen’s family and the Denali vampire coven are known to have eyes of this hue, a sign that they’re more heroic and “humane” than many of their allies. This diet is considered a sort of “vegetarianism” among vampires, despite still blood. That’s not to say that human blood is completely unappealing, however, as involving these vampires have to fight the urge to consume it if they come into contact with it.
With newborn vampires, their eyes are naturally a bright red color, almost glowing in the dark. This shockingly bright color is due to the former human’s own blood still coursing through their veins. This is why Bella Swan’s eyes become this color once she is turned into a vampire. If a newborn bloodsucker were to start feeding upon human blood, these bright red eyes would instead be darken to a rose-red color scheme.

Of course, abstaining from blood at this point would instead give them the gold eyes of the Cullen family. Vampires with the initial hue of red eyes will typically be alone, as they’re known for being more mentally irrational and hot-tempered. offline , those who are no longer newborns will instead take to congregating in covens and families.
Vampires in Twilight will have their eyes darken as their thirst for blood grows stronger. The same goes for the dark bruises under their eyes, which become even more pronounced as they wish for blood. Going without blood completely — regardless of the source — will further sap the light out of their eyes until they’re completely black. This process typically takes about two or more weeks to happen, but it presents a new danger.
Vampires in this state can go into a feeding frenzy, doing anything they can to get blood. This includes those who otherwise don’t consume human blood, who will be especially tempted by their need to stay alive. Unfortunately for all the actors in the movies, however, the contact lenses needed to portray these eye colors were rather uncomfortable, regardless of what their character’s diet was.