In an embodiment, a method in the manufacture of triple-patterning lithography masks, each mask represented by one of three colors, where each cell layout has exactly one polygonal pattern at one-half the different-color spacing from its left boundary, and exactly one polygonal pattern at one-half the different-color spacing from its right boundary. During placement of the cell layouts into a row, the method includes switching assigned colors in a cell layout to ensure that no two polygonal patterns of the same color in the layout are at a distance from each other less than the same-color spacing.