Future Water and Oil by Peter Pellikaan

A beautiful sleight-of-hand version of oil and water without any secret additional cards or gaffed cards. You start with four red-backed red cards and four blue-backed black cards. You fairly mix them and they immediately unmix. You exchange one card from the top of each packet the rest of the cards in each packet mysteriously follows. You show the cards from both sides. At the end with the colors separated they suddenly mix themselves into alternating red and black cards.