The Guardian (a left-of-centre British newspaper) did something similar in 2004, getting volunteers to phone voters in battleground states imploring them to vote Democrat. If anything, this boosted the Republican vote, as random foreigners telling citizens who to vote for is not a good look.
At the risk of explaining a joke into the ground your comment has more than one reference. The UK's two main parties have their colors flipped. Labour's color is red.