Best joke in the world

A Zebra dies and goes to heaven - as he gets to the Pearly Gates he sees Saint Peter and says "wait wait, there is some thing I need to know before I go to the great beyond - am I white with black stripes or black with white stripes?" Saint Peter rubs his chin and replies "humm, I do not know, you will need to ask the Great One" - he points to a stairway and bids the zebra to go hither.
When the zebra reaches the top of the stairs he is greeted by the Great One who says "Zebra, what is it you wish to know?" "Well..", says the zebra, "I have always wondered - am I white with black stripes or black with white stripes?" - - the Great One bellows down to the zebra "You are what you are - now be gone!"
When the zebra gets back to the Pearly Gates, Saint Peter sees him and excitedly asks "So zebra, what did the Great One tell you!?" "eh.." says the zebra, "he said - you are what you are". "Oh that's fantastic.." says Saint Peter "so you're white with black stripes!". The zebra says "what.. how do you know..?" "Because..." says Saint Peter, "..if you were black with white stripes he would have said you is what you is.."

How fast does a zebra have to run to look gray????