The search term you are looking for is "bezel".
There are many different approaches including:
- Tempered tinted glass (Graylight 31, etc)
- Paint on the back of tempered glass
- Paint on the back of plexi
- Printed adhesive vinyl on plexi
- Reverse-printed adhesive vinyl on the back of the plexi
- Printed bezel sandwiched between 2 sheets of plexi
- Black foam core board . . . .

Look through Project Announcements and you'll probably find a build or two that look like what you want.
Scott