The paper by Misha Vorobyev and D. Osorio explores the role of receptor noise in setting color thresholds in animals. They argue that psychophysical thresholds can only provide insights into mechanisms at a particular stage of the visual pathway if the noise at that stage dominates the noise in other stages. The authors model spectral sensitivities of di-, tri-, and tetrachromatic eyes under bright conditions, assuming that thresholds are set by color opponency mechanisms whose performance is limited by photoreceptor noise, with the achromatic signal being disregarded. They find that noise in the opponency channels is not statistically independent, making it impossible to infer more about these channels from psychophysical thresholds. The model predicts the performance of color vision in animals where physiological and anatomical data are available but no direct measurements of perceptual thresholds are available, making it widely applicable to comparative studies of eye design and visual ecology. The model is based on three assumptions: (1) color is coded by $n-1$ unspecified color opponency mechanisms, (2) opponency mechanisms give zero signal for stimuli that differ from the background in intensity only, and (3) thresholds are set by receptor noise, not by opponency mechanisms. The authors test the model using spectral sensitivities of six different animals and find that it agrees well with data for dichromatic, trichromatic, and tetrachromatic animals in bright illumination. However, the model does not always explain spectral sensitivities for dichromatic animals, possibly due to the influence of an achromatic channel. The paper concludes that receptor noise limits the accuracy of color vision in photopic conditions, consistent with other studies indicating that noise sets thresholds for other aspects of vision.The paper by Misha Vorobyev and D. Osorio explores the role of receptor noise in setting color thresholds in animals. They argue that psychophysical thresholds can only provide insights into mechanisms at a particular stage of the visual pathway if the noise at that stage dominates the noise in other stages. The authors model spectral sensitivities of di-, tri-, and tetrachromatic eyes under bright conditions, assuming that thresholds are set by color opponency mechanisms whose performance is limited by photoreceptor noise, with the achromatic signal being disregarded. They find that noise in the opponency channels is not statistically independent, making it impossible to infer more about these channels from psychophysical thresholds. The model predicts the performance of color vision in animals where physiological and anatomical data are available but no direct measurements of perceptual thresholds are available, making it widely applicable to comparative studies of eye design and visual ecology. The model is based on three assumptions: (1) color is coded by $n-1$ unspecified color opponency mechanisms, (2) opponency mechanisms give zero signal for stimuli that differ from the background in intensity only, and (3) thresholds are set by receptor noise, not by opponency mechanisms. The authors test the model using spectral sensitivities of six different animals and find that it agrees well with data for dichromatic, trichromatic, and tetrachromatic animals in bright illumination. However, the model does not always explain spectral sensitivities for dichromatic animals, possibly due to the influence of an achromatic channel. The paper concludes that receptor noise limits the accuracy of color vision in photopic conditions, consistent with other studies indicating that noise sets thresholds for other aspects of vision.