Surface finishes based on structural colors raise interest in product design and architecture in that long lasting colored surfaces can be produced with low risks if color fading. In this paper, aluminum surface are patterned through anodization with additional chemical post-treatment. This electrochemical technique is advantageous in that it is already industrially mature and enables the treatment of large surfaces. The resulting surface shows self-organized nanopatterns that lead to specific colored effects. In particular, colored effects similar to rainbow colors are observed in backscattering while the sample preserves its typical grayish metallic color when observed in direct reflection. Optical characterization of the sample have been performed and compared to optical simulations using Fourier modal method (FMM) method. A strong consistency between the simulation results and the experimental measurements has been obtained. It has been demonstrated that the color effects observed in backscattering are due to first order diffraction phenomena.