The technical problem to be solved by the invention is to change the thickness of the colored resin layer of the preform gradually in the upward or downward direction, by utilizing a tendency of gradual decrease in the thickness of the colored resin layer caused by the flow of the main resin inside the preform mold when the main resin and the colored resin are injected into the mold. The objects of this invention is to provide a biaxially drawn, blow molded bottle having new decorativeness created in which sophisticated color gradations associated with color density are created in the body of this bottle. The means of accomplishing this object involves adjusting the injection pattern including the time of starting and ending the supply of the main resin and the colored resin, and pressure or velocity profiles, reducing the thickness of the colored resin layer in the multi-layered molten resin fluid gradually at an upstream or downstream point of the flow, injection-molding the preform in which a color-gradated portion associated with the thickness of the colored resin layer has been formed, and biaxially drawing and blow molding this preform into a bottle having a color-gradated portion associated with the color density or color shade created on the body of the bottle.