The little slits at the mouth/chin area are supposed to be holes for breathing. I mean that's what I'd use them for, if you want them to look black just use more tulle (but in black) or some other kind of mesh. Unless someone is way to close to your face the slits should still look black.
You could also maybe get a balaclava mask if you really felt it necessary.
WIP to be debuted
San Japan: Laxus Dreyar (Fairy Tail)
Alamo City Comic Con: Hawkeye (Fraction run),
Street Vigilante Red Hood