An article at Phys.org recounts some amazing results of research that was done into why bird feathers take on the colors and patterns that they do.
It turns out that there are cells in the feather follicles that act like the ink jets in a printer. These cells inject colored pigments into the feather as it emerges from the follicle.
This is astonishing. What turns these cells on and off? What determines which colored pigments will be produced, when, and in what sequence? And how did a biological ink jet color printer ever evolve as a result of purely unintelligent, unguided processes?