The electron absorption spectra have been taken as a function of temperature (550-750°C) for melts with 0.9-1.6 mas.% of niobium of different oxidation degree within the wavelength interval between 620 and 360 nm. It has been shown that in addition to pentavalent and tetravalent niobium trivalent niobium ions could occur in salt mixtures under definite conditions. Niobium-containing salts have different colors, that depends on their ions valency. Coloration may be changed in the system transfer from a solid state to liquid one.