A method of producing a fibre or filament (10) by forming a substrate (11) in the form of an elongate core having a core axis. Coating the substrate directly, or indirectly, with a substance (13) having at least one electrically modulatable optical characteristic and associating with the substrate and/or substance, an electrical stimulation means (12) adapted to produce an electric field extending in a direction substantially parallel to the core axis or in a direction extending substantially circumferentially about the core axis, wherein the electric field electrically induces a change in the optical characteristic of the substance, thereby changing the visual appearance of the fibre or filament. |