From US Aids to Navigation, from the US Coast Guard:
You may have heard the phrase, “Red, Right, Returning.” This expression refers to the fact that when returning (entering a channel from the open sea or proceeding upstream), a boater must keep the red Aids on the right (starboard) side of the boat.
Red, Right, Returning. Except when it’s not.
The world has two marine aids to navigation systems, opposite of each other. From Cruising World:
Region A consists of Europe, Australia, New Zealand, parts of Africa and most of Asia. When entering a harbor in this region, marks to port are red and marks to starboard are green.
Region B consists of North America, Central America and South America, plus the Philippines, Japan and Korea. When entering a harbor in this region, marks to port are green and marks to starboard are red (red, right, return!).
This seems like something everyone should be taught in elementary school.