How the Eurasian Jay Expands its Color Palette by Optimizing Multiple Scattering

The production of structural color in nature is still incompletely understood. Multiple scattering exerts critical effects on synthetic disordered systems, but its effects on structural colors in natural materials are not yet well known. Here, electron microscopy, optical modeling, and biomimicry are used to show that variation in the thickness of the feather nanostructures creates periodic color variations in Eurasian jay wing covert feathers, with nanostructures within white feather regions being two times thicker than those in blue portions. This finding reveals that multiple scattering expands the natural color palette of the Eurasian jay by extending reflection to longer wavelengths in thicker spongy layers. Furthermore, it is found that the white color of Eurasian jay feathers is produced even in the presence of melanin due to a sufficiently thick spongy layer reflecting all visible wavelengths. Inspired by the Eurasian jay design solution, a one-step self-assembly method for mimicking periodic color variations in a synthetic context is described. Thus, the colors of natural color-producing materials are modulated by changing only the thickness of the materials, leading to multiple scattering effects.