Ratio R of integrated fluxes observed in the MuSCAT bandpasses uniquely determines the effective black body temperature of a flare. A black body of temperature T_eff is separately multiplied by the spectral response functions of the MuSCAT filters to produce the ratios R_j. We obtain different sensitivities for each filter pair: R(g,z_s) is theoretically more sensitive in temperatures below 5000 K while R(g,z_s) may be sensitive to temperatures up to 50 000 K.