The present invention provides a fluorescent marker ink coloring composition incorporating an optical brightener, a film-forming agent, an aqueous carrier, and a colorant. The optical brightener is an amphoteric distyryl fluorescent whitener which generates a special effect in the dried marking ink composition. The coloring composition can optionally include one or more of a humectant, a surfactant, a preservative, a drying agent, a pH regulant, a bittering agent or a fragrance. The present invention further provides a writing instrument comprising the coloring composition.