From the rulebook:
Spaces On The Game Board
Territories
The border colors of the territories on the game board show which power controls them at the start of the game. Each power has its own color and emblem (the United Kingdom controls the Canadian territories in addition to those with its own emblem). When the rules refer to the “original controller†of a territory, they mean the power whose emblem is printed on the territory.
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Once any formerly neutral territory becomes controlled by a major power, the rules regarding neutral territories no longer apply to it. It’s treated like any other territory, with the exception that it has no “original†controller (even if it was initially biased toward one side or the other).