Whoa - it was a good question!
What is it that you were thinking would be accomplished by using an ND filter? Perhaps you were looking to lessen the depth of field, or maybe you had something else in mind, or maybe there is something that you misunderstand. In any case, my reaction was: "I wonder why Chris thinks that might help?"
I would suggest more exposure, and a strong warming filter to help counteract the heavy cyan cast.
May we see a photo of the negatives themselves?