Cloud hadn't made much effort to help Zack with his choices or even criticize them because it was as he was following his friend around (and looking at black clothes, hm) that it occurred to him...he hadn't actually seen Zack in other clothes beyond what was required by the Shinra company.
It was an odd thought, and such an odd thing that he should be seeing his friend do something so simple as shop for clothes now. Would he have seen him do this in the future, anyway, if Zack had lived? What else could he have seen Zack do if they had survived the massacre together? He never gave it much thought -- but now, he would actually see it.
Zack had already gained five steps ahead of him when he popped out of his thoughts and he marched quickly beside him, hoping Zack didn't see him staring at a mannequin like a fool. "You done?" he asked almost hastily.