From Magic Hits (1937)
You write the name of a colour on a blank card and place it, writing unseen, in a small glass. You now introduce a packet of cards on each of which is printed a spot of a different colour. A spectator examines and mixes these then freely selects any one. This is placed in the glass beside your prediction, which is immediately removed. Your prediction may say, "RED." The chosen card is now taken from the glass and proves to have a red spot.
A dozen blank business cards.
A further dozen on on each of which has been printed (or has a sticker) a spot of a different colour.
A small glass that will hold a card neatly in an upright position.
Place a card with a red spot face down on top of the packet of blank cards.
1. Pick up the packet of blank cards, turn over the top two as one, and write the word "RED" on it. Tilt your hand up so the audience cannot see what you write. Lift these two cards off as one and drop them into the glass with the writing away from the audience.