Abstract: Method and related system for continuous and selective addition of a colorant and/or incompatible component into a radiation-curable coating composition comprising introducing a stock coating composition (primary coating, secondary coating, ink or matrix material) comprising a radiation-curable components (e.g., reactive acrylates) into a mixing zone having a primary inlet and an outlet; selectively adding at least one colorant (dye, pigment) and/or incompatible component (crystal-forming, hydrolyzate-forming, haze-forming) to the stock coating composition upstream of the mixing zone outlet; mixing the at least one colorant and/or incompatible component and stock coating composition in the mixing zone to provide a radiation-curable finished coating composition; continuously applying the finished coating composition onto an optical fiber; and curing the finished coating composition.