This is an interesting question to consider, because at various stages in this excellent novel it appears as if Conrad seems to condemn European culture for its colonialism whilst at the same time claiming it to be superior. Note how Marlow, early on in this story, seems to introduce this ambivalence about European culture and colonialism by comparing European colonialism to Roman colonialism:
What saves us is efficiency--the devotion to efficiency. But these chaps were not much account, really. They were no colonists; their administration was merely a squeeze, and nothing more, I suspect. They were conquerors, and for that you want only brute force--nothing to boast of, when you have it, since your strength is just an accident arising from the weakness of others.
Note the way that European colonialism is saved through its efficiency, but at the same time Marlow still goes on to condemn colonialism in all of its forms, whether or not it is based on efficiency. Thus I think we need to be careful in terms of trying to second guess Conrad's allegiances in this novel, as they, like so much else in this brilliant text, seem to be shrouded in ambivalence.