Ordered structures and void formation in systems of highly charged spherical macroions are investigated using the Sogami potential. The crucial feature of the treatment is the salt fractionation effect; Sogami theory combined with the Dirichlet boundary condition (constant surface potential) yields a definite prediction for the distribution of simple electrolyte between the macroion-rich and macroion-poor regions. The treatment is restricted to the extreme case of an equilibrium between an ordered structure and voids. The voids are found to be stable in the range between alpha kappa = 0.816 and alpha kappa = 3.05, where a is the radius of the particles and kappa is the inverse Debye screening length. In this range, added simple electrolyte fractionates between the macroionic crystals and the voids, accumulating strongly in the voids. Added electrolyte does not fractionate outside this range, leading to an extraordinary regime below alpha kappa = 0.816 and to a homogeneous liquid-like structure above alpha kappa = 3.05. Within the range, the hypothesis that the relevant interaction kappa in the crystals is determined solely by the fractionated simple salt leads to a definite prediction for the variation in the lattice parameter with added salt. This prediction is in quantitative agreement with recent USAXS measurements and with a physically realistic value for the surface potential of the charged spheres. It is noted that the standard DLVO theory of colloid stability has nothing whatsoever to say about these interesting phenomena.