1. A digital image-processing method for conducting a color gradient, said method comprising the steps of: (a) constructing a draft enclosed by an inner closed curve and an outer closed curve; (b) dividing said draft into a plurality of regions, each of which is enclosed by said inner closed curve, said outer closed curve, and two control lines constructed by respectively connecting a reference point located within an inner area defined by said inner closed curve with two control points located on said outer closed curve, wherein said plurality of regions are integrated to form said draft; and (c) introducing an operation to bring about a color gradient effect in each of said plurality of regions.