Look around you-color is everywhere. The clothes we wear, the food we eat, the posters with which we decorate our rooms; indeed all of our surroundings, natural and man-made, abound with color. From prehistoric times people have been fascinated with color; from cave paintings to the latest computers, color has been our constant companion. The Palette of Color monograph series enables high school chemistry teachers to challenge students to explore the chemistry behind dyes. Each monograph examines a different class of dyes and investigates the chemistry using principles common to most high school chemistry curricula. Hands-on, problem-solving activities involve students in answering questions posed about the dyes and their uses. Indigo and inkodyes are used to illustrate how vat dyes are synthesized and used. Until the end of the 19th century, all colors were obtained from natural sources, but today the number of synthetic colorants exceeds 7,000. One class of these colorants, the vat dyes, contains not only the oldest natural dyes known, but also many important synthetic dyes. This class of dyes is studied in this monograph.