Methods and apparatus are provided for applying a colorant material to the surface of a plastic insulation material which has been applied to an elongated material such as a metallic conductor (22) or an optical fiber which is being moved at any of a wide range of speeds along a path of travel. The colorant material is applied by nozzles which are staggered along the path of travel and which direct the colorant into engagement with the plastic insulation material at different radial directions. A first plurality of nozzles (46--46) each cause the colorant to be in a spray pattern (45) which is in the area of a plane. Advantageously, those nozzles cooperate to stabilize the conductor and prevent undulations thereof as the conductor is moved along its path of travel. A second plurality of nozzles (50--50) cause the colorant to be in a solid conical pattern (53). The first and the second pluralities of nozzles are effective to cause substantially all the surface area of the plastic insulation on successive increments of length of the conductor to be covered with the colorant material.