One or more zero-order diffractive pigments (ZOP) having both a particle distribution matrix material, and a layer of material in or on such a matrix material and having an index of refraction higher than that of the matrix material, and having a diffractive grating structure with a period in the range of 100 to 600 nm, which is smaller than the wavelength of light reflectable thereby in the zeroth reflection order. In such ZOPs the index of refraction of the matrix material is usually at least 0.25 less than that of the material of the layer, and the layer is typically of a thickness between 30 and 500 nm.