Depletion-induced phase separation in mixtures of charged silica particles and nonadsorbing polymer near theta conditions (polystyrene in dimethylformamide) was studied. The colloid polymer size ratio q was varied through the particle size and the electrical double layer thickness (kappa(-1)) through addition of lithium chloride (LiCl). The dependence of the phase boundaries, and the nature of the separated phases, on q and kappa is reported and is found to be in good agreement with recent theoretical predictions (Gogelein, C.; Tuinier, R. Eur. Phys. J., E 2008, 27, 171-184).