Using a carefully justified development of Debye-Huckel theory for highly asymmetric electrolytes, one finds that a region of expanded phase instability, or miscibility gap, can appear for charge-stabilized colloidal suspensions at high charges and low ionic strengths. It is argued that this offers a straightforward explanation for the observations of void structures and other anomalies in such suspensions in this region. The nature of the interface between coexisting phases, and general arguments that many-body attractions form a key part of the underlying physical picture, are also examined. The present analysis may also generate new insights into old problems such as coacervation in oppositely charged colloid or protein-polyelectrolyte mixtures, and suggests interesting new possibilities such as the appearance of charge density wave phases in colloidal systems in the vicinity of the critical solution points. (C) 2000 American Institute of Physics. [S0021-9606(00)51010-1].