Well, there used to be a character on Citrine, Drift, who was Zero's friend. But then he had a heart game and Drift was affected really badly and his relationship with the rest of Citrine got really rocky, to the point he started staying at Sterling using a glass key that Zero had gotten for him.

And...well, Ace's dislike of Citrine is basically due to that incident. |Db It has very little to do with the team itself and more to do with him being overprotective of Zero and having a personal dislike for Drift. So that whole time that was happening, Ace's thought process was like:

hate Drift
-> hate Drift for making Zero miserable and unhappy
-> hate reasons for why Drift is making Zero miserable and unhappy
-> hate Citrine for being part of why Drift is making Zero miserable and unhappy.

And then after that was over Ichiru showed up on Citrine and it was pretty much the same thing over again except in past tense, because Ace had prior knowledge of what Ichiru's done to Zero in the past. So now Citrine has basically cemented in his mind as "team where things that hurt Zero and make Zero unhappy show up" and that is enough to bias him against Citrine.

I'm sorry Annabeth, Ace is not actually that reasonable a person after all. '-'b

Rose on Cat? :o