The Color of Her Panties — Piers Anthony

In fact, Gwenny Goblin, Che Centaur and Jenny Elf are just about the only creatures on Xanth who have been spared the sight of Mela Merwoman's undergarment -- preoccupied as they are with helping Gwenny beat out her awful half-brother Gobble for chiefship of the goblin horde. But first they must master space and thyme . . . and find the fabulous egg that sits between the Roc and the hard place. While Mela -- who would gladly relinquish her oft-viewed undies for a new husband -- joins the Adult Conspiracy . . . and quickly discovers the power of a perfect pair of panties!