A coloring agent which can be substantially completely decolored either through a treatment by a low concentration of chlorine type decoloring agents such as chlorine and hypochlorite or through a biological treatment usually employed in sewage treatments. The coloring agent is a certain group of polymethlyne compounds having at both the ends of the polymethyne chain pyrazolone structures. A composition comprising at least one of the coloring agents and additives in solution or solid form suitably used for coloring toilet bowl flushing water.