Nitrogen-doped titanium dioxide (N-doped TiO₂) is attracting continuously increasing attention as a material for environmental photocatalysis. The N-atoms can occupy both interstitial and substitutional positions in the solid, with some evidence of a preference for interstitial sites. In this study, N-doped TiO₂ is prepared by the sol–gel method using NH₄OH and NH₄Cl as N ion doping agents, and the physical and photocatalytic properties with changes in the synthesis temperature and amount of agent are analyzed. The photocatalytic activities of the N-doped TiO₂ samples are evaluated based on the decomposition of methylene blue (MB) under visible-light irradiation. The addition of 5 wt% NH₄Cl produces the best physical properties. As per the UV-vis analysis results, the N-doped TiO₂ exhibits a higher visible-light activity than the undoped TiO₂. The wavelength of the N-doped TiO₂ shifts to the visible-light region up to 412 nm. In addition, this sample shows MB removal of approximately 81%, with the whiteness increasing to +97 when the synthesis temperature is 600oC. The coloration and phase structure of the N-doped TiO₂ are characterized in detail using UV-vis, CIE Lab color parameter measurements, and powder X-ray diffraction (XRD).