Color Production in Blue and Green Feather Barbs of the Rosy-faced Lovebird

We study experimentally and theoretically the coloration mechanisms of blue and green feather barbs in the rosy-faced lovebird (Agapornis roseicollis). Structural characterizations reveal that both the blue and green barbs contain a similar rod-connected amorphous diamond-structured photonic crystal (RAD-PC), producing basically a non-iridescent blue structural color. Numerical simulations show that the existence of a photonic pseudogap in the photonic density of states of the RAD-PC is the physical origin of the non-iridescent blue coloration. The green color in the green barbs is a mixed color coming from the blue structural color in the RAD-PC and the yellow color in the cortex layer that contains a yellow pigment. The optical function of the yellow pigment for achieving a saturated green color is discussed. The interesting coloration mechanisms unraveled may help us get in-depth understandings of the ingenious strategies of color production in nature and valuable inspirations as well.