smokescreen

A box with a transparent front is filled with a dark, opaque liquid. Inside the box are light-colored (and possibly fluorescent (i.e. Day-Glo)) flat objects that can be moved toward or away from the front of the box by actuators. These objects could be in the form of the segments of a seven-segment display (hence the category) or a low-resolution matrix similar to the flip-dot displays such as are used on buses and signs. Actually, the bistable magnetic actuators used in flip-dot displays would be usable for this. Other suitable actuators could be muscle wire, air bladders, wax motors, etc.

An advantage over flip-dot/flip-segment is that it can do grayscale.

37/212

P.S. I am shocked that this idea title was available. I was just going to use the subtitle as the title, but it seemed too long, so I came up with that.