This is a great question, which I engage audiences in regularly. I first
wondered the opposite: With projectors becoming so bright, we have the
ability to project with the ligths almost all the way up. What does that say
about what the color a blank screen should be, white or black? I wondered if
white should be the new blank? But each time we do an experiment, we all
agree that a dark screen is better than a white one--the white screen is too
harsh.
Now you ask the opposite: In a dark room, what should be the normal
backdrop, as opposed to the "blank." And you could certainly make the
argument that a white background would be too bright in a dark room. But I
just don't think you can generalize about this because no two "dark" rooms
are ever alike. I would ask you to scrutinize why you want the room to be
dark; do you really need to simulate movie-like conditions?
This question, or its unanswerability, argues for an ounce of preparation,
two slide masters, and careful adherence to color schemes. This would allow
you to adjust on the fly to conditions that you think warrant a switch from
one to the other.
