1. An image color determining device comprising: a ground color presence detecting section for determining a presence of a ground color of a target image based on image data relating to the target image; a ground color region specifying section for specifying a ground color region in a color space when it is determined that the ground color is present by the ground color presence detecting section; a ground color determining section for determining whether or not the image data to be determined is a ground color region based on the ground color region specified by the ground color region specifying section; and a ground color replacing section for replacing the image data determined as the ground color region by the ground color region determining section with a predetermined color.