In Publisher, you can control keepaway traps, overprinting, and knockouts throughout the publication. Or, you can specify overprinting or knockouts for selected objects.
Publisher uses keepaway traps to trap text reversed out of a rich black background.
Rich black is defined as a color that contains the percentage of black specified by the keepaway threshold plus one or more additional process inks. By default, Publisher applies a keepaway trap to any process color with 100 percent black plus any percent of another process ink. You can change the keepaway trap threshold to apply keepaway traps to colors with less than 100 percent black ink. Knockouts For all other objects, including nonblack objects, Publisher knocks out color behind all foreground objects. You can turn off overprinting for black lines, fills, and imported graphics that cannot be color separated or that have been recolored to black in Publisher, and change minimum text size for overprinting.