  The effective pair potential between mesoscopic charged particles in a
neutralising background medium takes a Yukawa form $\exp(-\lambda r)/r$ with
screening length $\lambda^{-1}$. We consider a dilute suspension of such Yukawa
particles dispersed in a solvent with correlation length $\xi<\lambda^{-1}$ and
show that the Yukawa interaction is `screened' if the pair potentials between
solvent particles exhibit Yukawa decay with the same screening length
$\lambda^{-1}$. However, if the solvent pair potentials are shorter ranged than
the solute Yukawa potentials, then the effective potential between pairs of
solute particles is `unscreened', i.e. the effective potential between the
solute particles is equal to the bare potential at large particle separations.
