I would simply call them and ask.

Did you get any answers on this yet? Looking at the Lutron website, it appears that the Midnight is part of the Satin colors and so is a matte black and the regular Black is gloss. If you're still working with this, a lighting store that stocks or special orders Lutron would have the complete color sample chips, for both the Satin (20 colors) and Gloss (7 colors). Or perhaps you can order the sample chips from the Lutron website.