Previous studies have suggested that orange pigment in the color patterns of male guppies is a cue for female choice. This paper describes a manipulative experiment designed to test this hypothesis. The color patterns perceived by females were manipulated by varying the color of light used to illuminate the experimental aquaria. Orange light dramatically reduces the conspicuousness of orange spots to human observers, and probably also to female guppies. As in previous experiments, female guppies discriminated among males based on differences in the extent of orange pigment, under white, blue, and green light conditions. Under orange light, however, females no longer appeared to discriminate on the basis of orange spots. These results support the hypothesis that orange spots, rather than other correlated characteristics, are a basis for female choice under normal lighting conditions.