What color is the fog in "Heart of Darkness"?

Surprisingly, the first time the fog is mentioned, no color is given. However, as the narrative proceeds, we're specifically told that the fog is white. It also seems solid at that point. In fact, we're told: "When the sun rose there was a white fog, very warm and clammy, and more blinding than the night. It did not shift or drive; it was just there, standing all round you like something solid." That indicates that whiteness restrains action in this novel, making the fog a metaphor.