Purple is the best color, no question. It can accelerate into a second turn power drain, and using drain and discard can completely control the game with no chance to lose.
This game is TERRIBLY imbalanced. There was obviously no testing to see if players could make decks with degenerate strategies.
Here is a hint to beat any opponent, use magistrate's council, then spam mana drain and myrken spy. You can completely deplete your enemy's resources and never allow them to come back.