Ishida usually colors Mutsuki’s skin a little darker then Kaneki’s. All of these things put together I can’t see the person on the magazine cover as Mutsuki. I don’t think that Ishida has drawn anyone other then Kaneki/Haise for a magazine cover, maybe with him but not on their own. I might be wrong about that and please correct me if I’m wrong. If it was a volume cover, it would be more likley that it would be someone other then Kaneki. Thats just my thoughts and your welcome to disagree with me.