Without a pic, it's extremely difficult to ID your fish, but there are only a few "all black" damsels. Here are a couple of links with pics to peruse through, to hopefully help you with an ID:
Damsels
and I suspect your fish may be one of these:
Pomacentrus aquilus
Pomacentrus
or from your description, less likely:
Neoglyphidodon melas
Neoglyphidodon
And it's not unheard of (but not common either) to find a domino damsel without spots:
Dascyllus trimaculatus
Dascyllus