Several mechanisms may contribute to regional differences in vertebrate pigmentation. In the embryo, alterations in the determination or migration of melanoblasts from the neural crest affect the number or distribution of pigment cells in the skin (reviewed in Reedy et al. 1998). Within hair follicles, paracrine signals control the type of pigment made in specific regions of the body or at specific times during the hair cycle (reviewed in Furumura et al. 1996; Barsh et al. 2000). Finally, movement of pigment granules within melanocytes or from melanocytes to keratinocytes makes use of cellular machinery that is shared by a variety of cell types, but that can vary in different regions of the body (reviewed in Marks and Seabra 2001). However, for all of these mechanisms—white spotting, pigment-type switching, and melanosome biogenesis—more is known about the identity of the molecular components than their spatial and temporal control.