In the Art of book it mentions that they had the idea of a double bladed with one blue blade and one red, it would be interesting if Rey were to end up getting it.
Meh, not a fan of double bladed lightsabers with different colors. It would symbolize Rey walking the line between light and dark, though, but I'd rather have her wield a purple saber then. It's sleeker and more subtle than 2 different colors.
Actually, I wouldn't mind Rey using a different color from the traditional green or blue. If not a purple saber, an amber/yellow/orange saber would be a nice change.