Dear friend, usually the whites of our eyes should be white. But some people may have yellow whites. If they got an infection on their liver, they may have yellow whites. If they smoke heavily, the whites of the eye could be tint by the yellow smokes so the whites of the eye will become yellow.
Once I saw black eyeballs in a film called SUPERNATURAL. I think the whites of our eyes will not turn black at a moment. So I guess the actors may wear some kind of colored contacts and this kind of colored contacts can make the whites of our eyes black or yellow which may totally depend on which kind of colored contacts you will choose. You can consult in an optical shop nearby to find whether there is a kind of colored contacts which can make our whites of the eyes yellow.
Aging and too much exposure to UV lights can lead to yellow whites. If you want to make the whites of your eyes yellow, you can stay at the outside without a pair of sunglasses. But I will not suggest you to do that for too much exposure to the sunlight will lead to eye problems. Macular degeneration is a kind of eye disease many senior citizens may suffer from.