Anodizing of aluminum generates a nanoporous alumina layer comprising cylindrical nanopores extending essentially perpendicular to the substrate. Visual observation of such nanoporous layers shows a colored specular reflectance consistent with reflectance spectrum measurements. Such structural colors raise interest in particular for producing non-fading colors. However the optical behavior is complex and requires specific characterization setups and modelling approaches. A morphological and optical characterization of nanoporous anodic alumina has been performed and enabled to draw the chromatic paths. Moreover, the optical behavior has been compared to numerical simulations of optical properties using the Fourier Modal Method, thus demonstrating the impact of short-range order and long-range disorder on the formation of structural colors in these partially ordered nanostructures.