Calculated reflectance spectra, optical contrasts, and color evolution of the mica flakes. (a) Calculated reflectance spectra of mica (colored lines) and gold (black lines) in the structure shown in the inset as a function of the wavelength of visible light. Mica thicknesses are 0 nm (black lines, bare gold), 10 nm (red lines), 30 nm (blue lines), and 50 nm (green lines). Gold layer thicknesses are 20 nm (continuous lines) and 300 nm (dashed lines). Inset: schematic representation of the layered structure analyzed. (b) Optical contrast in reflection mode between the mica and gold parts of the sample as a function of the wavelength of light for the same cases considered in (a). Inset: ratio between the contrasts for the two gold layer thicknesses considered. (c) Optical contrast in reflection mode as a function of mica thickness for three representative wave lengths, 475 nm (blue lines), 550 nm (green lines), and 650 nm (red lines), and two gold layer thickness, 20 nm (continuous lines) and 300 nm (dashed lines). (d) Evolution of the mica color (lines) as a function of its thickness in the xy chromatographic space for the case of semitransparent (black line) and opaque (red line) gold substrates.