Final answer:
The green over red over green banded buoy should be left on your port side when returning seaward in US waters to stay in the preferred channel.
Step-by-step explanation:
When returning seaward in US waters, you should leave the green over red over green banded buoy on your port (left) side to stay in the preferred channel.
In the United States, red and green lateral markers are used to indicate the sides of the channels. When heading seaward, green buoys should be kept to your left and red buoys to your right, according to the conventional 'red right returning' rule.
However, since the mentioned marker has specific vertical bands with green at the top and bottom with red in the middle, it indicates a preferred channel mark. In this case, the buoy would suggest that keeping it to your port side would guide you through the preferred channel as you head out to sea.