When the slave hunters see Huck rowing his canoe to shore, they stop him to ask him who is on the raft.
“Well, there's five niggers run off to-night up yonder, above the head of the bend. Is your man white or black?”
Huck tells the slave hunters that the man on the raft is white. This is his first lie. Then he elaborates rather subtly, implying that the man on the raft has small pox.
When the slave hunters confront Huck with the blunt question, Huck "admits" that they have come to the right conclusion. He tells them the man on the raft is his father and he has small pox and no one so far has been willing to help tow the raft in to land.
The men leave Huck and the raft alone then after offering some advice.
This moment in the novel relates to Huck's crisis of conscience. He is tempted to turn Jim in because the society and its laws mandate that this is the right thing to do. However, turning Jim in would be a betrayal of his friend and his deeper sense of what is right.
When the men ask Huck if the other man on the raft is white or black, Huck is presented with a moral choice...With some hesitation, he chooses once again to stick to his promise to Jim.
This dilemma recurs throughout the novel until Huck finally decides to accept hell as his fate if it means being loyal to a true friend.