What Am I?

Two zebras are talking and one asks the other, "Am I black with white stripes or white with black stripes?" The other replies, "Well I don't know. You should pray to God about that and ask him." So that night he did and God replied, "You are what you are." The next day he said to the other zebra, "I still don't understand what I am because God just said, You are what you are." The second zebra responds, "You must be white with black stripes or else God would have said, Yo is what yo is."