1. A colorimetric method comprising: performing colorimetry on color patches to acquire colorimetric values; and determining whether or not the color patches that have been subjected to the colorimetry are target color patches that should undergo the colorimetry based on the colorimetric values and reference values, the color patches being arranged in a matrix form, the colorimetric values being acquired by measuring color values of the color patches along the rows or the columns of the matrix, a plurality of different colors being assigned in a predetermined order to the color patches arranged along the rows or the columns of the matrix, and the determining further including determining a decoded value based on one of the colorimetric values in response to measuring a color value of one of the color patches, and determining whether or not the color patches that have been subjected to the colorimetry are the target color patches that should undergo the colorimetry based on whether or not the remainder of a row number or a column number of the color patches that have been subjected to the colorimetry relative to a number of the different colors matches the decoded value.