Time correlation functions of concentration fluctuations are obtained from hydrodynamic fluctuation theory extended to ternary systems. The coupling between the concentrations of the different species is accounted for and leads naturally to symmetric correlation functions unlike those previously reported. The time correlation functions of concentration fluctuations incorporating the effect of thermal noise are used to obtain the initial scattering intensity of ternary polymer-polymer-solvent systems undergoing spinodal decomposition. It is shown that the scattering function is represented by a sum of three exponentials. Single exponential growth is predicted under certain conditions which appear to have been met in the limited experimental data available.