Digital and letterpress: are not opaque. For the ink to be visible, pick an ink that is darker than the paper.
White ink: is an exception to digital printing and is opaque and will show up on darker paper.
Foil: is also opaque and will show up on paper that is darker than the foil.
Blind embossing: is pushed up out of the page without ink. It is better for bold text and images.
Blind debossing: is pushed down into the page without ink. It works for fine or bold details.

Should you pick something that is not feasible, a design consultant will contact you to discuss other alternatives.