Structural colour
Colour produced by microscopic structure that bends and reflects light, not by pigment.
Also: physical colour
Most colour comes from pigments, which absorb some light. Structural colour works differently. Surfaces with features about the size of a wavelength of light, such as thin films, layers or grids, reflect some colours strongly and cancel others. Blue butterfly wings, kingfisher feathers and beetle shells are examples; grind them up and the colour vanishes, because the structure is gone. Blue pigments are rare in animals, so most animal blues are structural. Such colours do not fade in light, and engineers are trying to copy them for paints without dyes.