done for 'spot' printing. Cyan, Magenta, Yellow and black. The term is 'color shift'. Happens in all printing. Sometimes results in an effect that looks like double printing. One place it happens regularly is on the surround to the Palms 'A MALOOF CASINO RESORT' which I suspect is made up of 3 or even all 4 colors. I have a $5 Hagar here which looks as though the words are missing due to a shift in one of the colors.