Momcats can eat their young if they feel overwhelmed in the numbers delivered, or if one of the kittens is ill. If it doesn't smell right, mom will destroy it or move it out of the nest for a predator to take it. Keep you eyes on the other kittens, it is possible they might become ill as well.
Please get your momcat spayed after these kittens are weaned. That will help her out a great deal. When you say one is really pink- what exactly do you mean? If you pick up this pink kitten is it warm or cold in your hand, or is it hot? Is there fur?