The correct answer is C) light characteristic. The light characteristic, which refers to the pattern and timing of a buoy's flashing light, does NOT indicate the preferred channel when approaching a preferred-channel buoy. Instead, the preferred channel is indicated by the color of the uppermost band on the buoy, as stated in answer choice D. The other answer choices are incorrect because the color of the light (A) and the shape of an unlighted buoy (B) can provide information about the type of buoy, but they do not specifically indicate the preferred channel. The light characteristic (C) is not the correct indicator for the preferred channel.