PREPRESS Three will get you seven

Using enhanced GCR (gray component replacement), it’s possible to use just three different screen angles in seven-color printing without risking color shifts. Black, as the dominant color, is assigned to 45°. The six chromatic colors, cyan, blue, magenta, red, yellow, and green, are alternately assigned to 165° and 105°. Then, each hue can be generated using only three colors: black, which provides the gray component; and two neighboring colors.

For example, all printable hues between red and yellow can be created using black and these two process colors. A maximum of 10% of a complementary color can be added to darken the color without causing color shift. Essentially, only three colors are printed on the same part of the image.