Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
but if it is black then that is what it is: Blackground.
Anyway, no Satin or Matte finish, or even Flat will not be weird looking. Might even be better.
To see how these might look hold up something that is not shiny as a background: A black towel, or other fabric, a piece of construction paper or similar.
The plastic sheet backgrounds from fish stores are usually shiny, at least equivalent to Gloss or High Gloss.
I have used all sorts of materials, and I do not think the Gloss or lack of it is very important.