1. An image data processing device capable of outputting image data to at least one image display device, the image data processing device comprising: a first image acquisition unit for obtaining first image data; a first image output unit for outputting the first image data to the at least one image display device; an attention area acquisition unit for obtaining an attention area composed of one or more arbitrarily specified pixels from the first image outputted to the at least one image display device; a color chart display unit for displaying a color chart whose hue and chroma are gradually changed toward around the color corresponding to the image data of the attention area; a selected color information acquisition unit for obtaining arbitrarily selected color information from the displayed color chart; a color parameter calculation unit for obtaining a plurality of combinations of the attention area and the color information corresponding to the attention area and calculating a color parameter on the basis of the obtained plurality of combinations; a color conversion unit for converting the color of the obtained image data on the basis of the color parameter; and a second image output unit for outputting the image data whose color is converted, to the at least one image display device as a second image; wherein the first image output unit outputs the first image to a first image display device, the color chart display unit outputs the color chart to a second image display device and the second image output unit outputs the second image to the second image display device; further comprising a color temperature setting information acquisition unit for obtaining color information of a white point of the first image set on the basis of respective color temperature adjustment functions of the first image display device and the second image display device, wherein the color parameter calculation unit calculates the color parameter on the basis of a combination of the obtained attention area and the color information, and color information obtained by the color temperature setting information acquisition unit.