A first color value of a printing medium under a first light source which emits first light including light in an ultraviolet region and at a first temperature is obtained from either a measured data table or a measurement section. A second color value of the printing medium under the first light source and at a second temperature different from the first temperature is obtained from either the measured data table or the measurement section. A color value of the printing medium at a viewing temperature, which is different from the first and second temperatures, is estimated from the obtained first and second color values.