A solid colorant dispensing unit configured to dispense at least one charge of solid spherical colorant particles in a time-controlled way, the solid colorant dispensing unit comprising: - a supply container comprising a free end portion that is provided with a nozzle that is configured and arranged to dispense said at least one charge of solid spherical colorant particles during operation of the solid colorant dispensing unit, said solid spherical colorant particles having the following properties: - a number average particle size; and - a number particle size distribution, wherein a ratio of the standard deviation of the number particle size distribution to the number average particle size of the solid spherical colorant particles is less than 25%, preferably less than 22% and more preferably less than 20%, wherein the number particle size distribution is determined with light scattering with fully automated image analysis according to ISO 13322-1:2004, Particle size analysis - Image analysis methods - Part 1: Static image analysis methods by the use of an analyzer; the nozzle comprising a dispensing outlet having a diameter taking into account the number average particle size of the solid spherical colorant particles; and characterized in that the solid colorant dispensing unit comprises: - a control assembly that is configured and arranged to control dispensing of said at least one charge of solid spherical colorant particles in a time-controlled way by taking into account said properties of said solid spherical colorant particles and the diameter of the dispensing outlet of the nozzle. - a supply container comprising a free end portion that is provided with a nozzle that is configured and arranged to dispense said at least one charge of solid spherical colorant particles during operation of the solid colorant dispensing unit, said solid spherical colorant particles having the following properties: - a number average particle size; and - a number particle size distribution, wherein a ratio of the standard deviation of the number particle size distribution to the number average particle size of the solid spherical colorant particles is less than 25%, preferably less than 22% and more preferably less than 20%, wherein the number particle size distribution is determined with light scattering with fully automated image analysis according to ISO 13322-1:2004, Particle size analysis - Image analysis methods - Part 1: Static image analysis methods by the use of an analyzer; the nozzle comprising a dispensing outlet having a diameter taking into account the number average particle size of the solid spherical colorant particles; and characterized in that the solid colorant dispensing unit comprises: - a control assembly that is configured and arranged to control dispensing of said at least one charge of solid spherical colorant particles in a time-controlled way by taking into account said properties of said solid spherical colorant particles and the diameter of the dispensing outlet of the nozzle. - a number average particle size; and - a number particle size distribution, wherein a ratio of the standard deviation of the number particle size distribution to the number average particle size of the solid spherical colorant particles is less than 25%, preferably less than 22% and more preferably less than 20%, wherein the number particle size distribution is determined with light scattering with fully automated image analysis according to ISO 13322-1:2004, Particle size analysis - Image analysis methods - Part 1: Static image analysis methods by the use of an analyzer; - a control assembly that is configured and arranged to control dispensing of said at least one charge of solid spherical colorant particles in a time-controlled way by taking into account said properties of said solid spherical colorant particles and the diameter of the dispensing outlet of the nozzle.