Thats a good thought, but no, the frosting sheet can be applied to dark colored toppings, thats not an issue. What can't be applied to dark colored toppings is DIRECT TO FOOD printing, where no frosting sheet is involved, and thats because the direct to food printing colors will be muted against a dark background (your dark topping). But when using a frosting sheet which has a white background, the colors will show up against the white sheet, even if there is a dark background behind the sheet.