Low cost and ease of fabrication are important factors for solar-thermal applications in energy-efficient buildings. This contribution reports the influence of oxygen on structure, optical properties and chromaticity of TiAlOxNy thin films prepared by DC magnetron sputtering. It is an extension of a previous study on colored solar-thermal absorbers based on titanium-aluminum nitride. The purpose is to investigate the possibility of using TiAlOxNy as middle layer to achieve a gradient effect. The results reveal that the structure and optical properties of the TiAlOxNy coatings are sensitive to the oxygen content under certain sputtering conditions. The ratio of oxygen/nitrogen of 0.7:10 is the most appropriate to form the crystalline structure of TiAlON. The optical constants of TiAlN and TiAlON were deduced by fitting the experimental data. It shows that both the refractive index (n) and the extinction coefficient (kappa) are decreased when oxygen is introduced to form titanium-aluminum nitro-oxide. The gradient effect can be achieved and controlled by adjusting the ratio of oxygen/nitrogen flow during the process to enhance solar absorptance while keeping the desired color appearance. (C) 2011 Elsevier B.V. All rights reserved.