  Today colloids are employed in various products from creams and coatings to
electronics. The ability to control their chemical, optical, or electronic
features by controlling their size and shape explains why these materials are
so widely employed. Nevertheless, altering some of these properties may also
lead to some undesired side effects, one of which is an increase in optical
scattering upon concentration. Here, we address this strong scattering issue in
films made of colloids with high surface roughness. We focus on raspberry type
polymeric particles made of a spherical polystyrene core decorated by small
hemispherical domains of acrylate. Owing to their surface charge and model
roughness, aqueous dispersions of these particles display an unusual stability
against aggregation. Under certain angles, their solid films display a
brilliant red color due to Bragg scattering but otherwise appear completely
white on account of`strong scattering. To suppress the scattering and induce
transparency, we prepared films by hybridizing them either with
oppositely-charged PS-particles that fit the length-scale of the raspberry
roughness or with quantum dots. We report that the smaller PS-particles prevent
raspberry particle aggregation in solid films and suppress scattering by
decreasing the spatial variation of the refractive index. We believe that the
results presented here provide a simple strategy to suppress strong scattering
of rough particles and allow for their utilization in optical coatings,
cosmetics, or photonics.
