Hi, Definitely a pumpkin, cucurbita pepo. Will turn dark green and then orange, variety...not sure. Looks like it is still growing since it still has light green color streaks. Thick stem and elongated shape makes me think phat jack cross/mix. Keep it watered well, and if it is a phat jack it could be really nice sized, also be on the look out for powdery mildew, that can really damage leaves late in the season.