Symbolism, Imagery, Allegory
Before leaving Black's apartment and walking out to likely death, White explains the full depth of his despair to Black. He says:
"The truth is that the forms I see have been slowly emptied out. They no longer have any content. They are shapes only. A train, a wall, a world. Or a man. A thing dangling in senseless articulation in a howling void. No meaning to its life. Its words. Why would I seek the company of such a thing? Why?" (139)
White means that the forms have been emptied of meaning—they seem inorganic, just shapes with no greater design or purpose to them. From Black's perspective, White probably sees things this way because he's been emptied of purpose and content. In other words, he sees a world that reflects his own suicidal frame of mind.
Perhaps surprisingly (given how much these two banter), White might not disagree with this take. But he would still maintain that the worst possible picture of the world is still the most correct—so the fact that his mind's emptied of purpose just means that it's emptied of illusion, and is therefore more accurate.