In BG-siluet, the screen becomes monochrome: the background becomes white, while the elements become black. Whenever an element and/or object has motion, it makes a little blur, just like BG-light, but shorter. Objects, blocks and the grids are always black. Elements that have motion will be colored in slightly darker colors (some can have greater color saturation; such as acid), otherwise, it blackens.
When Scale is set to normal and the player zooms in to anything above scale-1, the background will become white, but all elements can still be seen. This is used by many uploaders to view glass, while still distinguishing it from other elements used in the upload, instead of every element being represented by black like in the original Powder Game.
A player named Dome, along with other players, has suggested a similar idea like this. There is a possible glitch, using Copy-Paste, sweep the selection area over an upload in BG-siluet, it is almost as if it was turned off and back on.
Most uploads can be uploaded in BG-siluet to give a confusing feeling.