I have 2 good suggestions for you.
1. Take a peice of thin plywood and cut out in the middle where you screen is, then keep doing about 3 layers of this, each about a hlf inch in to give a 3d efect to your display, just screw or glue the peices together, goup, sand, and paint a few coats of black.
2. Take a peice of plexi glass, and on the back side put masking tap around the area the monitor will be, and spray paint the rest glossy black, when you put it on, all will be black except ypur monitor area.