Dark slide backgrounds

General comment on slide presentations. The fad of using a black 
background for slides removes an important visual aid for the presenter:
some light reflected on the audience's faces. The presenter has a clue 
how well the audience is following. For me, that is most important.

Also the black (or even dark blue) background is more conducive to sleep.
The presenter will not know, unless someone is snoring!

Regards/Harvey