I think that when directors go for the white background, that indicates that they are trying to create some illusion. That is what does not work. Illusion really is not part of an online reading.
This is not part of a f2df reading. If the characters are in period costume or have props in addition to their script--the attempt at illusion is a sign that the director is focusing on thing a reading cannot do, rather than the things it can.
Love Letters and Encores aside, generally when people try to turn readings into productions, it does not work.