Provided is a technique for coloring without any problem with waste water or stability of color development or deposition. A plating solution for coloring characterized by containing a molybdate and a carboxylic acid having one or more carboxyl groups and one or more hydroxy groups and having two or more carbon atoms or a salt thereof, and having a pH of 4.5 to 7.5. A method for coloring a member to be plated characterized by electrolyzing the member to be plated as a cathode in this plating solution for coloring.