To describe the rich phenomena in dilute dispersions of highly charged colloidal particles, it is necessary to modify the long-range electric part of the DLVO potential. The screened Coulombic potential of pure repulsion obtained from the Helmholtz free energy in the DLVO theory is replaced by a new screened electric potential with a long-range attractive tail derived from the generalized Gibbs free energy, which is identified with the total sum of chemical potentials.