Researchers at Yale University have found that some of the brightest colors in bird feathers are created by structures similar in origin and composition to that of beer foam. Unlike most colors in nature - which are produced by pigments - the bright blue colors of Bluebirds and Blue Jays are actually produced by sponge-like nanostructures formed in quite the same way as beer foam. From the article:

They compared the nanostructures to examples of materials undergoing phase separation, in which mixtures of different substances become unstable and separate from one another, such as the carbon-dioxide bubbles that form when the top is popped off a bubbly drink. They found that the color-producing structures in feathers appear to self-assemble in much the same manner. Bubbles of water form in a protein-rich soup inside the living cell and are replaced with air as the feather grows.

Not surprisingly, this discovery and further work could lead to new advances in materials science:

We have found that nature elegantly self assembles intricate optical structures in bird feathers. We are now mimicking this approach to make a new generation of optical materials in the lab.