Color vision in the California sea lion (Zalophus californianus).

Three California sea lions were trained to discriminate between a colored stimulus and two shades of gray in a 3-fold simultaneous choice situation. The colors blue, green and red were tested against shades of gray varying from low to high relative brightness. All animals distinguished blue from gray; two animals also distinguished green from gray; but none discriminated between red and gray. Our data suggest that California sea lions have dichromatic color vision. Their ability to discriminate colors in the blue-green part of the spectrum could be a physiological adaptation to their aquatic coastal habitat.