For membrane switches, it usually with a Graphic Overlay and with circuits ( silver), and has 2 kinds keys. "Die pressing" and metal dome.
also it can design widows ( transparent or translucent) in the pad. This often used in some system or equipment that for human to control.
Attached a picture to show the layers of membrane switches. also the 2 kinds of keys type.
For Graphic overlay, it is just a front panel, which is sample as top layer of membrane switch, and will back with rear Adhesive ( 3M).
It usually has windows ( a picture show the difference of the window of transparent & translucent.