Question

How come some examples of structural coloration (like peacock feathers) only shows certain colors (blue-green to violet) but others (like pearls) shows any color if looked at from the right angle? (Answer should include talking about the spacing between reflecting structures)

Answer 1

color in bird feathers is primarily due to the way they selectively reflect certain wavelengths of light. The phenomenon is similar to the way a thin layer of oil on the surface of water can appear to be a variety of colors.

In the case of feathers, the different reflective surfaces are closely-spaced and the wavelengths of the reflected light can interfere with each-other—constructively and/or destructively. This causes very bright iridescent colors that appear and can change dramatically with only the slightest movement of the bird and its feathers.