  The phase behavior of colloidal particles embedded in a binary fluid is
influenced by wetting layers surrounding each particle. The free energy of the
fluid film depends on its morphology, i.e., on size, shape and connectivity.
Under rather natural assumptions a general expression for the Hamiltonian can
be given extending the model of hard spheres to partially penetrable shapes
including energy contributions related to the volume, surface area, mean
curvature, and Euler characteristic of the wetting layer. The complex spatial
structure leads to multi-particle interactions of the colloidal particles.
  The dependence of the morphology of the wetting layer on temperature and
density can be studied using Monte-Carlo simulations and perturbation theory. A
fluid-fluid phase separation induced by the wetting layer is observed which is
suppressed when only two-particle interactions are taken into account instead
of the inherent many-particle interaction of the wetting layer.
