  We calculate the interaction potential between two colloids immersed in an
aqueous mixture containing salt near or above the critical temperature. We find
an attractive interaction far from the coexistence curve due to the combination
of preferential solvent adsorption at the colloids' surface and preferential
ion solvation. We show that the ion-specific interaction strongly depends on
the amount of salt added as well as on the mixture composition. Our results are
in accord with recent experiments. For a highly antagonistic salt of
hydrophilic anions and hydrophobic cations, a repulsive interaction at an
intermediate inter-colloid distance is predicted even though both the
electrostatic and adsorption forces alone are attractive.
