Peacock feathers are an example of one of the most extraordinary patterns in the biological world. They are often present in mythology, and have been a stimulus for Charles Darwin to develop the concept of sexual selection during evolution. The beautiful tail is produced by patterning processes at several levels. Each feather exhibits unique color patterns, by means of a combination of distinct pigment cell arrangement (chemical color) and organelle spacing (optical interference, physical color). At the feather tract level, each feather is well positioned and grows to a specific length. The eyespots are regularly spaced in the large plane of tail feathers, shining like hundreds of eyes. At a higher level, there are strikingly different plumages in different body regions. Finally, these showy feathers are sex hormone dependent. They are generated from modest brown feathers via molting row by row during puberty. The molecular mechanisms of these processes remain for us to decipher, and will work like a Rosetta Stone to reveal to us the fundamental principles of pattern formation. Caption and photo by Cheng-Ming Chuong. Los Angeles Arboretum, CA. USA.