Anolis is a diverse genus of small arboreal lizards that utilize a colorful expandable throat-fan (dewlap) for visual communication. The environment the lizard lives in has influenced the coloring of these dewlaps in different species. Species that occupy shaded habitats tend to have yellow dewlaps while those that inhabit brighter habitats tend to have red or orange dewlaps. Modelling these dewlap colors in a perceptual color space predicts that red is more visible against a green background than yellow, yet most anoles have yellow dewlaps. However, quantal fluctuations under low lighting may result in more receptor noise for some colors. This can affect the discrimination of one color from another by changing the distance between them in perceptual color space. Modeling that takes receptor noise into account predicts that yellow colors will be more visible than red under low light and less visible under high light. We used a color perception assay to test whether a red or yellow stimulus against a green background was more visible to the lizard under different light intensities, mimicking a dewlap appearing in a forested or open habitat. We flashed red, yellow, and green (control) stimuli, and if the lizard detected a change, indicated by a swift head or eye movement towards the stimulus, a positive response was noted. Our results mirrored those predicted by the receptor noise model, suggesting that yellow is more visible under low light while red is more visible under high light. Since light intensity has a greater effect on the discriminability of red against green than yellow against green, this may account for the prevalence of yellow dewlaps in shaded habitats. In a second experiment we tested the relationship between dewlap and background brightness, independent of color, to see if dewlap brightness directly, influences detectability.