Biologists and physicists alike have long been fascinated with colorful tissues such as the fiery red feathers of hummingbirds and blue skin of poison arrow frogs. While most research has focused on the communication functions of these colors, they may also affect heat retention. For example, thermal resistance and heat gain from the sun is greater for dark than white skin. Colored tissues are diverse, however, and we know little about their thermal properties. Here, we propose to investigate these properties in two speciose and colorful groups of endotherms (sunbirds) and ectotherms (agamid and cordylidae lizards) that inhabit climates ranging from cold/dry to hot/wet. First, we will compare thermally-relevant reflectance between different color types, including those based on pigments like carotenoids (yellows, reds) and melanins (black, brown, grey), white colors, and iridescent colors produced by highly organized tissues. We predict that melanic colors will retain the most heat, and that the angle-dependent reflection of iridescent colors will enable dynamic heating. Second, we will determine how morphological features, ranging from the molecular to millimeter scale, produce these diverse effects. Finally, we will use evolutionary methods to compare color and climate, predicting that darker animals will inhabit cooler areas. These results will inspire new multifunctional materials, clarify the evolution of colors, and have implications for effects of climate change.