The flag for UTC -4:00 uses the colours green, white, black, and yellow. As Cancer is the 4th sign of the Zodiac its use here reflects a four hour shift from GMT. Likewise, as this time zone is westward it uses the Western Zodiac.
Nations and places that fall under Cancer Time include: Canada's Atlantic Isles except for Newfoundland, Bermuda, Puerto Rico, Dominican Republic, the Eastern Caribbean, Guyana, Western Brazil, and Bolivia.
Note that during spring and summer the Eastern Half of the United Sates switches to Cancer Time, but in the fall reverts to Leo Time.