As I've been continuously aggregating prior art and other background information for my research, I've really enjoyed tracking one specific thread on biomimicry and bioinspiration. A couple of my favorites:
Fish cloaking - Some silver scaled fish have crystals inside their scales which affect how light reflects off their bodies, making them much harder for predators to see.
Firefly lanterns - The pattern of a firefly "lantern" (the apparently correct name for glowing insectoid hindquarters) couples light out very effectively, and might make LEDs and displays more efficient.
Butterfly scales - More well known...the scales of butterfly wings are capable of incredible color mixing.