The invention relates to a process of preparing polymer particles which comprise an effective amount of at least one colourant, a polymer matrix and secondary particles distributed within the polymer matrix. The process comprises the following steps: A) Preparation of an emulsion of a polymer formed from a monomer blend in an aqueous phase and Formation of the secondary particles in the aqueous phase B) Addition to the aqueous phase of an effective colouring amount of at least one colourant C) Dispersing or dissolving the colourant in the aqueous phase and D) Subjecting the emulsion to dehydration in a spray-drying unit.
