[Xylemon]

When I opened it with ImageMagick it appears to be a transparent PNG. Very clever trick, as it seems to use Twitters black background when viewing an image to achieve the effect.

[kevinwang]

So it's unrelated to the gamma trick in this article?

[pygy_]

Yes, it is.

[Syrup-tan]

In that case, how does the room disappear?

[myhf]

The room is drawn with translucent black pixels that show up on any light background. The stars are drawn with translucent white pixels that show up on any dark background.

[kristopolous]

look closely --- it's still there.