What is Color Register? 

Color register is the alignment between image elements of different colors in a printed image. Because the separate colors are normally applied at separate print locations, or even at separate times in the printing process, some mechanical control must be used to assure that each of the colored elements has the same relative position as seen in the original image. This relative positioning is especially important if the printed reproduction is composed of small “dots”, as in half-tone image. In such an image, even relatively small misalignment of the dots will be perceived by most viewers as an ‘incorrect’ reproduction.