The film concerns a virtual-reality game, with scenes shot in both the real world and the game. The game world is absolutely drenched in what that article calls "intangible sludge" - everything is a murky brown, and settings are usually fairly spartan, containing little other than the player characters and enemies. The real world, on the other hand, looks naturalistic, albeit shabby, given that this is set in crapsack cyberpunk Eastern European city.
Or at least, you think it is. Until the final act of the film, when the protagonist gains access to a "Class Special A" level in the game - which is simply modern-day Warsaw, shot straight, like a documentary, and as such is crammed with life and colour. After an hour and a half of the various shades of beige in the earlier levels and the real world, your brain has recalibrated itself to that, and so this perfectly normal scene assaults you with its hyperreality. It's a trick, and a simple trick, but it's amazingly effective!