Provided is a radiation-curable, optical glass fiber coating composition containing at least one radiation-curable oligomer or monomer, and at least one chromophoric indicator selected so as to be susceptible to destruction of its chromophoric characteristic upon exposure to radiation and present in an amount which becomes substantially colorless when exposed to a level of radiation sufficient to cure said radiation-curable, optical glass fiber coating composition, wherein said at least one chromophoric indicator has a color which is distinguishable from a base color of said radiation-curable, optical glass fiber coating composition in cured form. The invention also provides a method of making the coating composition. The invention further provides a coated optical glass fiber and a method of making a coated optical glass on a fiber drawing tower. Also provided is a cable and telecommunications system.