A system for introducing flowable additive e.g. colorant from a syringe into paint varnish, woodstain or the like contained in a closed container provided with an inlet into the container which inlet is closed by a closure. The inlet is openable by insertion of the nozzle of the syringe into the inlet which thereby ensures that the nozzle of the syringe is correctly located in the inlet before expulsion of the additive commences.