A research team simulated phase separation in colloidal suspensions. By treating colloid particles as undeformable highly viscous liquid droplets suspended in a solvent, they predicted the kinetics of colloid demixing — separation into a particulate phase – with high efficiency. A microscope study of real colloidal suspensions confirmed the accuracy of the model, which crucially included hydrodynamic (solvent-mediated) interactions between particles. This parameter-free model could be applied to other soft matter, biofluids, and colloid material design.