Always create a Solids Foundation layout with a white border so that the layout doesn't bleed. This is an evolution from earlier iterations of this foundation. The only exception to this rule is when an ad "floats" among editorial content or other ads, in which case a (0.25 pt) black line should be included at the edge of the ad.
Note: Take care that the printer you work with maintains the integrity of equal channel widths. Don't accept a trimmed piece in which the white channel borders appear to the naked eye to be different widths.