If you wish to use black areas in your project, please note that they should ideally be in 4 colours.

For a saturated, dark black, create a new colour with the following properties:
100% Black, 70% Cyan, 70% Magenta, 70% Yellow

If you select a normal one-colour black here, you should note that the black will not be saturated but rather more of a greyish colour after printing.