A children's party magician has a large-format coloring book, but as the pages are flipped through for the audience, it is clear that the book is completely blank. The magician says a magic word and flips through the book again. This time, the book has pictures ready to be colored. The magician says another magic word, and the pages of the book have now all been colored in.
The magician says that the kindness and goodness of all the little children have colored the book's pages, and as long as they stay pure and innocent the book will be forever in bloom. At this point, if an older teenage sister or similar individual walks into the room, the fast thinking magician can say something like, "Ooops! All spoiled!" and show the pages blank again.
The magic is all in the edge of the book and how the magician holds it. The spine of the magic coloring book has four ink-filled bladders -- one each for cyan, magenta, yellow, and black. The pages of the magic coloring book are blank, but if one of the ink bladders is squeezed, ink flows into tiny capillaries within the blank pages, filling them and making them appear colored. Releasing the bladders sucks the ink back into the spine, making the pages blank once again.
By squeezing just the black bladder, the magician makes the book look ready to color. Squeezing all four bladders gives the book a look of having been completed. If the magician is performing for a printing or typography convention instead of children, individual color bladders can be activated, allowing for all sorts of jolly color matching, trapping, and press-check jokes to be told.