The illustrations for Bill Peet's first twelve books were made using a process called color separation. This was done to save the publisher money. In this process, four separate drawings are made for each illustration: black, blue, red, and yellow. The black drawing was made first with India ink and black pencil. The three other colors were drawn with black pencil. Bill Peet did not know what the finished drawings would look like in color until he received a proof from the printer.