Indigo Bunting

Like all other blue birds, Indigo Buntings lack blue pigment. Their jewel-like color comes instead from microscopic structures in the feathers that refract and reflect blue light, much like the airborne particles that cause the sky to look blue.
Bunting plumage does contain the pigment melanin, whose dull brown-black hue you can see if you hold a blue feather up so the light comes from behind it, instead of toward it. (Cornell)