The work aims to investigate the oxidation of TC4 titanium alloy processed by laser cladding in open environment. TC4 coatings were prepared with the laser inside powder feeding technology in various argon gas flows. The surface and cross-section morphology, microstructure, elements distribution, phase compositions and microhardness of TC4 coatings were analyzed by SEM, EDS, XRD and Vickers Indenter, respectively. With the decrease of argon gas flow, the surface color of coatings evolved from silvery white to yellow, blue and dark grey. From XRD analysis, the color changes were mainly attributed to the colored titanium oxides. Yellow was caused by yellow TiO, blue was associated with blue Ti2O3, dark grey was white Ti2O3 related to thick oxide structure. In the environment without argon flow, the coating surface was rough and the oxide film was thick and porous and had gap with coating. With the increase of argon gas flow, the coating surface became smooth, and the oxide thickness gradually decreased. The density and the adhesion to the coating were good. The microstructure changed from lath-like structure to needle with the increased argon gas flow, which was related to cooling rate. When the coating was blue, the hardness became higher, indicating that the oxygen diffusion depth was large and the oxygen content was high. The cladding coatings appear brilliant color changes in various argon gas flows and the blue can be regarded as critical color between the acceptable and unacceptable oxidation degree of the oxidized titanium alloy.