The correct answer is B) white lights. Safe water buoys, also known as fairway buoys, are used to mark the center of a navigable channel or fairway. According to the U.S. Coast Guard's navigation rules, safe water buoys must show only white lights, which indicate that the water is safe to navigate on either side of the buoy. The other answer choices are incorrect because flashing green lights (A) are used for port-hand (left-side) markers, flashing red lights (C) are used for starboard-hand (right-side) markers, and yellow lights (D) are not used for any standard navigation buoys in the United States.