Colloidal clustering in an evaporating aqueous droplet was investigated by means of optical microscopy. The colloids were negatively charged paramagnetic polystyrene microspheres coated with a monolayer of the protein streptavidin. The dynamical process of the colloidal clustering was characterized quantitatively by the radial distribution function. The experimental results demonstrate that the clustering process goes through stages wherein the cluster is compactified and a colloidal crystal is formed at its core. Moreover, by adjusting the external magnetic field acting on the magnetic colloids, we could investigate the influence of the repulsive dipolar forces on the colloidal cluster dynamics and the equilibrium distance between the colloids in the cluster.