  We propose that the behavior of asymmetric binary fluid mixtures with a large
class of attractive or repulsive interparticle interactions can be understood
by mapping onto effective non-additive hard-sphere models. The latter are best
analyzed in terms of their underlying depletion potentials which can be exactly
scaled onto known additive ones. By tuning the non-additivity, a wide variety
of attractive or repulsive generalized depletion potential shapes and
associated phase behavior can be ``engineered'', leading, for example, to two
ways to stabilize colloidal suspensions by adding smaller particles.
