A multilayer thin film filter is disclosed an organic dielectric layer (104) serving as a spacer layer in a Fabry-Perot structure. The dielectric has embossed regions of varying thicknesses wherein the thickness within a region is substantially uniform. Each different region of a different thickness produces a different color (C1, C2, C3) (shift). The size of one of the embossed adjacent regions is such that the color (C1, C2, C3) of said one region is uniform and cannot be seen by a human eye as different in color from the uniform color of an adjacent region thereto, and wherein the color within a region can be seen with magnification of at least 10:1. This serves as a covert color coding system useful as a security device.