Don't get mad at me, but I think it's the quality of your film's emulsion. Snow is really dificult to shoot for a camera, so I assume the film is not picking up the right tones all over the shot. If you'd do this on for instance Fuji Velvia (E6 film), the colors would be much blue-er, but much more evenly that this. I can't really reccomend using color negative film - the whole c41 process was developed as a film for easy/quick color printing for consumers. The pro films like HQ100/160 are in a way upgraded consumer films. (Don't get angry ;) But I'm not completely sure that that is the real reason....perhaps someone else knows ? Btw, in case you know the photo.net site, a search for that film with that problem might turn up some answers.