The colors of various butterflies often originate from photonic nanostructures, found in the scales covering their wings. Such colors are called structural colors. The color generating scales are composed of a nanostructured chitinous material containing air voids, which causes the structural colors through light interference. We performed optical spectrum simulations utilizing full 3D Maxwell equation calculations on model structures to reveal the connection between the 3D structure and the optical spectrum. Our simulations showed that different scattering processes determine the spectrum in different wavelength ranges. For large wavelengths (>350Â nm) the optical reflection can be well described by a corresponding effective multilayer model and the peak positions are well represented by a simple first Born approximation. One has to include second order scattering processes inside the layers, however, in order to correctly reproduce the small wavelength side of the spectrum (<350Â nm). This means that such details of structure, as the shape of the air voids determine the small wavelength spectrum.