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 . <EOS>