27Lies

Because Axel and Roxas both consider Xion to be her own person, or as much as they consider anyone in the organisation a person, they see her for her self, which is the appearance of black hair and way too sulky for her own good face. So Axel sees Xion as Xion, and mentions the resemblence to Namine because she looks like Kairi, who looks like Namine (at least they're supposed to, I don't see it) and he hasn't met Kairi yet. At first I'd imagine he'd see her as the hooded figure the player sees at the beginning, which despite meaning to have no gender, still looks decidedly female. Once they become friends he sees her for her. This is backed up by in some of the scenes as when they are from Roxas' point of view Xion has her hood down and when it changes to Axel's POV she has the hood up. It's not a mistake as I originally (and stupidly) thought.