1. A printing data generating method for determining color loss for a color printer, comprising steps of: generating first printing data for forming a color loss determination section by printing at least one letter, a graphic, or a symbol in a prescribed printing area on a surface of a print medium using a single coloring agent; generating second printing data for printing a background portion of the color loss determination section in the prescribed printing area by overlaying a plurality of coloring agents that are each individually different in color from the single coloring agent so that the background portion is the same color as the at least one letter, graphic, or symbol; controlling driving of the color printer to print the first printing data and the second printing data; and determining that at least one coloring agent used to print the color loss determination section did not print if the print color of the at least one letter, graphic, or symbol is different from the print color of the background portion.