A new camera metric is proposed based, in concept, on the vision test devised by Davidson and Hemmendinger. The "D&H Color Rule" is a set of two linear patch arrays containing at most one match for near-normal color observers. The match selected by an observer can provide an indication of how that observer's color vision relates to others. Comparisons may be made to a group of interest, or more commonly, to a CIE Standard Observer. For this research, two image targets have been created, one physical and one virtual, each with a family of spectra related in much the same way as the colors in the original D&H Rule. These targets can be physically imaged or virtually modeled to predict camera RGB, and then CIELAB with a color profile. The camera can then be judged as to what degree its output matches that of a CIE Standard Observer. © 2018 Society for Imaging Science and Technology.