1. Process for the optical marking of a target region captured by a color measuring device on a measurement surface, comprising: reproducing on the measurement surface a two-dimensional color pattern which at each point has a clearly unique color value; aiming the color measuring device onto the measurement surface; measuring the color value of the target region captured by the color measuring device; calculating the local coordinates of the target region on the measurement surface from the measured color value; and reproducing an optical marker at the location on the measurement surface defined by the calculated coordinates of the target region, which marker visually identifies the location of the target region on the measurement surface.