What happens when a Flip card is played?
When a Flip card is played, everything switches from the Light Side to the Dark Side (or vice versa). The Discard Pile is flipped over (the card just played goes to the bottom), then the Draw Pile is flipped, and every player must flip their hand to the other side. This new side remains in play until another Flip card is played.
From the official Mattel GDR44 Uno Flip Card Game manual, page 1
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