This hue is inspired by the vivid cobalt-blue plumage of the bluebird, a color not produced by pigment but by microscopic keratin structures interlaced with air pockets that selectively scatter blue wavelengths of light. When white light strikes the feather, this nanostructure cancels red and yellow wavelengths while amplifying blue, sending the color back to the observer’s eye. The effect shifts with the angle of light, giving the feathers a luminous, shimmering quality against the bird’s warm chestnut breast. More than decoration, this structural blue may aid in species recognition and help attract mates.