1. An image forming apparatus comprising: input means for inputting an image having a plurality of colors; discriminating means for discriminating each of the plurality of colors of the image input from said input means; pattern generating means for generating a pattern image corresponding to the colors discriminated by said discriminating means; and image forming means for forming the pattern image, generated by said pattern generating means on a recording medium, wherein said image forming means forms the pattern image in a color associated with the colors discriminated by said discriminating means.