background.
The whiteness of your white depends on the fabric base chosen. The whitest whites are the poplin, sateen, twill, and the polyesters. The rest are varying degrees of off-white. The richness of the blacks depends on the fabric base. The polyesters (anything without "cotton" in the name) provide the closest to true black. Cotton poplin is the closest to black of the cottons. The rest will print closer to charcoal gray or "off-black." If in doubt, order a test swatch.