Metelli has proposed a model of the intensity relationships in perceptual transparency based on Talbot’s law of color fusion. Four constraints follow from the application of Talbot’s law. Experiments 1 and 2 show that violations of constraints i and ii adversely affect the perception of transparency, while violations of constraints iii and iv do not. Many common occurrences of transparency are in terms of subtractive, rather than additive, color mixture. The constraints derived from the Metelli model are also shown to hold for subtractive color mixture with a filter. An assumption of the Metelli model is that the degree of perceived transparency varies linearly with reflectance. Experiment 3 indicates that the degree of perceived transparency with “partim transparency” varied linearly, not with reflectance, but with lightness, a nonlinear function of reflectance. Experiment 4 indicates that judgments of the degree of transparency with “complete transparency” are based on stimulus relations that differ from those that determine whether the perception of transparency occurs. The results are discussed in terms of how the pattern of intensities relates to other stimulus information, such as figural configuration, in producing the perception of transparency.