Abstract: Color control strips of sheets in a multi-color printing press are monitored by a light beam which is reflected by successive increments of the patches of the strip and passes through the filters of a filter wheel. The thus obtained color density signals are stored in memories, one for each color and each capable of storing the entire density profile of a patch. When the memories are filled to capacity, the admission of each fresh signal entails the eradication of the oldest stored signal. The stored profiles are evaluated by a microcomputer which discards certain signals and processes the remaining signals to ascertain the boundaries between neighboring patches, the center of the patch following the last-ascertained boundary, and the color density at the center of such patch.