As the Collector, Mr. Turton is the head of the British civil administration in Chandrapore. He's an experienced administrator who has swallowed the British imperial project hook, line, and sinker. It's not just about controlling the land, the people, the wealth for Turton: it's also about using the British Empire to "civilize" the Indians, by force if necessary.
At his best, Mr. Turton moderates the flagrant racism of his subordinates because of his belief that the British are the more advanced people, and must thus act accordingly. The Bridge Party is, after all, his idea, and if he's not exactly friendly, at least he's polite. At his worst, well, even at his worst, Turton uses his power to ensure that his subordinates don't persecute the Indians and that everything is done by the book. He's not exactly the poster child for racial tolerance, but he's a good example of how the British civic ethic can prevent an individual from seeing his own worst prejudices.