So featureless, in fact, that you can't even tell where the walls, floor, and ceiling end—they all blend seamlessly together under the uniform light, so the chamber looks more like a white void than a room.Sometimes, the only indication that it's a void is the fact that the characters have something solid to stand on.As literal white voids represent some "other realm"—usually a result of a dream or crossing over to another universe—physical rooms that replicate this visual effect will have the same connotations.
Or, the white can represent sterility, making these rooms suitable for otherworldly hospitalization.
Or, it can represent the limitless possibilities of a blank canvas, so this room could be a currently-inactive holosimulator, or some other place where literally anything can happen.
Occasionally, there are a few pieces of furniture (color is optional) in the room for the characters to sit down and have a discussion. When this effect is produced unintentionally by poor description, it is a Featureless Plane of Disembodied Dialogue.
Often a sign of the Lazy Artist in Sequential Art when the background is missing.
You returned to your reading - and a moment later there it was again. But more and more, people are beginning to see them straight on and for longer periods of time.
You looked up quickly this time and saw the fleeting but distinctly human shape of the shadow pass quickly over the far wall... Some experiencers testify that they have even seen eyes, usually red, on these shadow beings.
Or was it something that seems to be a spreading phenomenon - apparitions that are coming to be known as "shadow people" or "shadow beings." Perhaps this is an old phenomenon with a new name that is now being discussed more openly, in part thanks to the Internet.
The diffused high-key light often makes this the opposite of Chiaroscuro.
See also Misery Lit for when a book presents the white void room on its cover to represent death.