The correct answer is D. No light. A lighted buoy to be left to starboard when entering a U.S. port from seaward will not have any light. This is because the United States Aids to Navigation System follows the standard IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) Region B system, where the preferred side for a vessel to pass a buoy is to its starboard (right) side. Buoys on the starboard side of the channel are unlighted, allowing the vessel to distinguish them from the lighted buoys on the port (left) side of the channel. The other options are incorrect because a white light, green light, or Morse code light characteristic would indicate the buoy is on the port side of the channel, which is the opposite of what is being described in the question.