Adult Orconectes virilis exhibit a variety of colors from yellow to blue to dark brown that are strongly correlated with habitat background color. We used field and laboratory experiments to examine both the proximate mechanisms and the possible functions of this color variation among populations of crayfish in northern Michigan. Field transfer experiemnts showed that adults can change color, brown morphs becoming blue and vice versa. Light penetration measurements at six field sites indicated relationships between differential wavelength penetration and the colors exhibited by crayfish in a habitat. Holding crayfish in water from different habitats induced color changes while feeding crayfish vegetation characteristic of different habitats did not produce significant color differences. Laboratory predation experiments, field enclosure experiments, and transfer mark-recapture experiments did not indicate any differential survival of morphs that matched or contrasted with the background.