Dark color? Could you please give more details? A female parakeet's cere is supposed to be brown, while a male's is supposed to be blue. How old is your parakeet? Did her cere just turn this color? What color was it before? Is she acting normal? Is their discharge from her nostrils? If so, is it clear or thick/colored? Are her droppings normal? I need more details before I can help, because I don't quite understand what's wrong. Maybe she scratched her nostril and hurt it?