Originally Posted by Cottontop
You forced me to do a little research, and unfortunately (I liked the Revolutionary War explanation), it seems Congress adopted "red, right, returning" in 1850. Port buoys were black, and only changed to green in the 1970s, after Coast Guard studies showed green to be more visible.
I didn't find anything explaining how the world came to have, generally, two opposite color systems.
Actually, I always liked the Revolutionary War explanation too.
I became more curious and found this reference
that speaks to the origins of buoyage systems and specifically states this about the beginnings of the US system.
"By 1846, Secretary of the Treasury Robert Walker admitted that buoys placed by local authorities under loose regulations, coupled with the lack of standardized colors and numbers, were practically useless. Congress, sensitive to complaints about the ATON system, began taking steps to correct the problems in 1848. It adopted the Lateral System for implementation nationwide. It is from the Lateral System that the familiar "right, red, return" has its origin."
Supposedly, the UK did not adopt green to starboard inbound until the 1970's when the IALA set up its international standard.
Prior to that it was black to starboard, mostly, with red to port, but that only really came in after WW2 - before then local harbor authorities did as they pleased.
As recently as the 1930's the buoyage in Harwich harbor, most definitely in England (the Mayflower's home port was Harwich) was "red to starboard inbound" just like the US system.
Nautical history and lore fascinates me.