Light-scattering contrast variation is used to study refractive index fluctuations in porous glass media (controlled pore glasses, CPG). The porous glass grains are dispersed in a nearly isorefractive cyclohexane/toluene mixture, fine tuning the optical contrast by temperature adjustments, Comparison of the scattering intensity as a function of the optical contrast with our contrast variation model for porous media reveals that the solid phase of the porous glasses is optically almost homogeneous. It is also shown that the scattered intensities as a function of the magnitude of the scattering vector are in fairly good agreement with the linearized Cahn-Hilliard theory for spinodal decomposition, in combination with the form factor of the porous glass grains. Refractive index autocorrelation functions, obtained by Fourier transformation of the scattering curves, clearly indicate structural ordering in a glass grain on length scales comparable to the interpore distance.