The physics of colour shifting

Optical coatings consisting of one ore more films of dielectric or metallic materials,
are widely used in applications ranging from mirrors to eyeglasses and interference
filters.
Many conventional dielectric coatings reley on Fabry-Perot-type interference,
involving multiple optical stacks of transparent layers with thickness of the order of
the wavelength to achieve functionalities such as anti-reflection.high-reflection and
interference.