Colors in animals can be produced either chemically by (usually diet-acquired, costly) pigments or physically by the constructive interference of light scattered by endogenous, cost-free, photonic nanostructures and sometimes as a combination of both. Fade-proof, saturated structural colors have evolved convergently in diverse animal taxa, including birds, insects and arachnids. However, given that the underlying nanostructures are overwhelmingly diverse in form and function, their characterization has suffered for over a century. I have pioneered the use of synchrotron Small Angle X-ray Scattering (SAXS) as a high throughput technique to structurally and optically characterize integumentary photonic nanostructures from hundreds of species across diverse animal orders in a comparative fashion. This led to the discovery of the first single gyroid crystals in biology within the iridescent green wing scales of certain papilionid and lycaenid butterflies, and recently in the feather barbs of the Blue-winged Leafbirds (likely driven by female preference for saturated hues). But broadly, this wealth of structural knowledge has led to the realization that these diverse photonic nanostructures share a unifying theme – they all appear to be self-assembled within cells by the co-option of fundamental intra-cellular processes: membrane invagination in insect scales and liquid-liquid phase separation in bird feather barb cells. In this talk, I will broadly summarize our current state of knowledge about the structure, function, development and evolution of self-assembled animal structural colors using examples from birds, butterflies, beetles, bees and tarantulas, including in the fossil record.