We analyze the core-shell structure of sterically stabilized hard sphere polymer colloids by optical contrast variation. Modified polymer particles are used which have the same refractive index as the suspending solvent. At low contrast, inhomogeneities in the core shell structure of the particles become apparent. The particle form factor is shown to be a sensitive function of the temperature due to the interplay of scattering from the core and the stabilizing layer. We explore the dependence of particle form factors on composition, radius, and temperature and rationalize our observations in terms of a simple core-shell model. By exploiting the sensitivity of the form factors we are able to independently study the two components of a binary mixture of polymer particles.