Color Monte by Emerson & West

One of the best-selling packet tricks of all time!

The magician relates how he lost bet after bet with a clever gambler using 3 cards. Two cards with a red spot and one with a blue spot are shown. Trying to guess where the blue spot is, the magician "loses" a dollar each time (the cards change to all blue spots, change back to red spots, etc).

After seven (!) amazing changes, the magician has "lost" $7.00. He puts one red spot and one blue spot card on the table and asks what color remains. Now it's a double or nothing bet. No matter what is said - the last card is turned over showing $14.00 printed on it!