Spherical colloids exhibit striking analogies to atoms and to small proteins. Unlike to atoms, interaction potentials of colloids can be modified by means of chemical surface modification or with the help of additives. This renders them a class of compounds which is highly suitable to investigate interaction patterns of proteins and to tune organization of colloids into highly ordered assemblies. We focus on the design of new colloidal systems capable of forming crystal-like assemblies while at the same time bearing specific optical properties. To give but an example, we currently prepare complex core-shell (polystyrene-polyacrylate) colloids, which are designed to be covered in a controlled way with Ag-nanoparticles. The final aim with complex colloids is to accomplish - in close collaboration with the Physics Department - particles with strong optical magnetism.