1. A change degree deriving device comprising: a receiving unit that receives an image obtained by capturing an object and a known color body including a plurality of color samples, the plurality of color samples including deterioration-series colors among colors used for the object, and each of the color samples having a known colorimetric value; a conversion rule generating unit that generates a conversion rule used to convert a color of the image received by the receiving unit into a colorimetric value in a device-independent color space based on the color samples included in the image received by the receiving unit; and a converting unit that converts a color of the object included in the image received by the receiving unit into a colorimetric value in the device-independent color space according to the conversion rule.