Abstract: The present invention relates to pigments comprising or consisting of a layer made of a material with an index of refraction that is higher than the index of refraction of the adjacent material by at least 0.25; whereas said layer has a zero-order diffractive micro-structure; whereas said layer acts as an optical waveguide and whereas said layer has a thickness between 50 nm and 500 nm; to processes for its manufacture and to its use. These pigments show a color effect upon rotation and/or tilting, and it is believed that this color effect is based on zero-order diffraction.