8 

Count down backwards, moving your poker chip ( ) one card for each number as you do so.

Example: If SEVEN is chosen, you count 7-6-5-4-3-2-1 and end up on the face-down card between the Six of Clubs and the Ace of Clubs.

If you end up on a face-up card, turn all face-up cards face-down.

If you end up on a face-down card, turn all face-down cards face-up.

Congratulations! As the name of the trick suggested, you chose the only red card.