Anion doping of tungsten trioxide by nitrogen is used to obtain electrochrome cathode material, the spectral transmittance of which can be controlled by the doping level. A series of samples was synthesized by reactive magnetron sputtering of a metal tungsten target in a mixture of argon, nitrogen and oxygen gases. Warm-colored tungsten oxynitride films were prepared at higher doping levels and characterized using scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy techniques. Optical properties were measured making use of transmission spectrophotometry and spectroscopic ellipsometry. These extensive experimental studies revealed an increase in absorption towards shorter wavelengths with increasing the doping level. At the same time, it was found that with increasing the doping level, the fraction of non-stoichiometric oxygen also steadily increases to half the total oxygen content. The imperfection of the doped material can stimulate its intercalation with electrolyte ions, accelerating the coloring/bleaching process and increasing the dynamical range between the dark and clear states, thus improving the consumer qualities of electrochemical materials and devices.