Earliest Common Map Key

There are multiple color codes like UCS, RCS and the like, and more recent ones have expanded to include just about variation of every country, its territories, dominions, protectorates and autonomous regions, including extinct or scifi/fantasy countries.

What was the earliest board-wide color scheme and why were these countries chosen?
 
There are multiple color codes like UCS, RCS and the like, and more recent ones have expanded to include just about variation of every country, its territories, dominions, protectorates and autonomous regions, including extinct or scifi/fantasy countries.

What was the earliest board-wide color scheme and why were these countries chosen?
See this wiki page: https://www.alternatehistory.com/wiki/doku.php?id=resources:map_colour_schemes
If you follow the link to UCS, that explains its background as the first AH.com colour scheme.
 
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