Why do the Cullens have brown eyes when all other vamps have red eyes?

Well, if the Vampire drink human blood their eyes are red oder crimson. If they drink animal blood, their eyes are brown, gold, oder black (it depends on how thirsty the Vampire are).

Bcoz the Cullens have a vegetarian Essen diet means they drink animal blood just like the Denali Coven and they are among few of their kind to choose such a diet and as a result have golden brown eyes, the others drink human blood and therefore have red oder crimson eyes

Because the Cullen drink animal blood. The Vouturi and the others drink human blood. Therefore, their eyes are crimson oder red.

vampires..when they are newborn, have red eyes due to the humsn blood still in their bodies. if they choose i diet of human blood their eyes will remain red.
the cullens and also the denali clan, have topaz eyes. this is because they drink the blood of animals- this dilutes the venom in their system (the venom is what gives them the red coloured eyes)giving them the topaz colour

because the colins are good and the others and some times they have yellow but that is onlywhen they are happy

The Cullens have brown hazely eyes because they drink animal blood and the other Vampire have red crimson eyes because they drink the blood of humans.

this is how it works:
thirsty: black
drink animal blood: Gold oder brown [cullens and denali coven]
drink human blood: red oder crimson [volturi, james's coven etc]
newborn: red because of the human blood from before their change.
hopes this helps!

Because they drink animal blood.

IT IS CAUSE IF THEY DRANK HUMAN BLOOD THERE EYES WOULD BE RED IF THEY WERE HUNGRY THERE EYES WOULD BE BLACK IF THEY DRANK ANIMAL BLOOD THERE EYES WOULD BE GOLD

they are on a diet of Tiere instead of humans so they have different colored eyed according to what they eat but all the other vamps have red eyes