Colors in organisms can be produced either chemically by pigments or physically by the interference of light scattered from biophotonic nanostructures or sometimes in combination. Fade-proof, vivid, saturated structural colors that have evolved over millions of years of optimization are an ideal source to look for natural solutions to our current technological challenges in optics, sensing, etc. and can provide facile biomimetic routes for eco-friendly materials synthesis for functional applications. However, given that the underlying nanostructures are overwhelmingly diverse in form and function, their characterization has lagged for over a century. I have pioneered the use of synchrotron Small Angle X-ray Scattering as a high throughput technique to structurally and optically characterize biophotonic nanostructures from hundreds of species, in a comparative framework. This has led to the understanding that all these diverse, mesoscale nanostructures share a unifying theme – they appear to be self-assembled within cells by bottom-up and directed processes.  I led the discovery of the first biological single gyroid photonic crystals in the iridescent green wing scales of certain butterflies that beautifully pre-empt our current engineering approaches and recently, within some bird feathers. The latter appears to be the first directly self-assembled single gyroid known to science and at the hard to achieve optical length scales. In this talk, I will broadly summarize our current state of knowledge about the structure, function, development and evolution of organismal structural colors in birds and insects, as well as discuss some future directions on how understanding the intracellular development of biophotonic nanostructures can lead to novel, eco-friendly routes to mesoscale synthesis for advanced applications from sensors, photonics, energy harvesting to catalysis.