In "Heart of Darkness" what color is the fog that engulfs Marlows' steamboat on the river?

The fog that Marlow's steamboat gets caught in is white. But the white fog in this case is not the opposite of darkness; it simply compounds darkness. Fog not only obscures but distorts: it gives one just enough information to begin making decisions but no way to judge the accuracy of that information, which often ends up being wrong. Marlow's steamer is caught in the fog, meaning that he has no idea where he's going and no idea whether peril or open water lies ahead. He and the pilgrims he is carrying are frightened they will be attacked in the fog. One man states,‘We will all be butchered in this fog". Thus the confusion and darkness of the river is intensified by the fog.