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1. The thermal melanism hypothesis (TMH) predicts that dark (low skin reflectance) individuals are at an advantage in cool climates as they heat faster and reach higher equilibrium temperatures than lighter (higher reflectance) individuals. However, tests of the TMH have yielded mixed support, especially in ectothermic vertebrates. 2. Most studies to date have been undertaken at small spatial scales or using a few, closely related populations or species. Here, we therefore examine the TMH at large scales in heliothermic lizard species, testing two of its major predictions and a corollary thereof, using standard and phylogenetically corrected analyses. 3. First, we test the prediction that skin reflectance and climate variables such as mean annual temperature (MAT) and global solar radiation are positively related across species. Second, we determine whether a positive relationship exists between skin reflectance and …