Blue had practically no playable creatures.  Amphin Pathmage is fine I think, but Accursed Spirit gets the job done better against non-black.

I guess a question that we can ask ourselves is if there is a specific colour we expect to see split more often.  If our opponents don't split black, then 2 of their 3 decks won't contain black and intimidate might increase in value.

I looked through Nixon's decks after constructing mine, but before posting this note and noticed that the colour combinations are different.  One difficulty that I had with this UB deck was finding cheap creatures that did something (so pairing blue with a colour other than black would probably be better).