Thermodynamic modeling of eight copper-containing pyrotechnic flames was carried out to investigate a suggestion that the emitter of blue light is Cu3Cl3. In seven of them the dominant Cu species was CuCl and in three, Cu3Cl3 was essentially absent (mole fraction <0.000005). This is consistent with previous spectroscopic studies showing that the blue light emitter is CuCl. The calculated adiabatic temperatures of flames from formulations reported to give good to excellent blue colors ranged from 1660 K to 2500 K. This is inconsistent with statements in the literature that the flame temperature has to be below 1500 K. An eighth formulation, specifically formulated to give a high temperature blue flame but reported to give a poor color, had a flame temperature of similar to 2900 K and the dominant Cu species was atomic Cu.