The present invention relates to effect pigments having a color flop comprising metal oxide-coated SiO.sub.2 flakes having a uniform layer thickness, where the color flop runs through all four quadrants of the a,b color coordinate system (CIELAB L,a,b system). The present invention likewise relates to processes for the preparation of these pigments in which SiO.sub.2 flakes having a uniform layer thickness are coated with metal oxides, and to the use of these pigments in cosmetics, paints, coatings, plastics, films, in security printing, in security features in documents and identity papers, for coloring seed, for coloring foods or in medicament coatings and for the preparation of pigment compositions and dry preparations.