The performer displays a children's magic coloring book with black and white pictures, the kind you just paint over with water, and the pictures magically appear. The children are asked to try and color the pictures by real magic, using their imagination, instead of water. They are told to rub their fingers on the colors on their clothes, and throw the colors at the book. When the book is now displayed, all the pictures have been fully colored. The performer congratulates the audience on their magic abilities, and excellent artistic talents.
However, he states he has to perform the same trick again for another show the next day, and since they have colored all the pictures, there will be no pictures left for the children to color at his next performance. He asks his audience to help him erase some of the colors with imaginary "magic" erasers. The children pantomime rubbing off the colors, and when the book is flipped through again, it is found to be entirely blank.
Obviously they used too much magic. The performer requests them to draw some of the pictures with imaginary pencils. When the book is again flipped through, the black and white pictures are back in the book, ready for the next performance.