A device used to accurately measure the tristimulus values of a particular color. Essentially, a colorimeter conists of a vision field—either located through an eyepiece or directly with the eye—which displays, on one side, the reference—or comparison—color, produced using red, green, and blue light beams, the proportions of each one constituting a particular color are indicated on the device. On the second half of the vision field is the color to be tested, and either a human observer or a photoelectric detector is used to evaluate each color for matching purposes.