Pics of the actual bellies would help, along with some more shots of side pattern from the side. Perhaps Acid/Confusion/Static? I don't see a lot of speckling, so I'm doubtful on that but it's an idea to explore and look at the pattern more thoroughly to see. There is a Black Belly morph, but I don't think they look at all like that. The pattern sort of resembles Trick/Hurricane in areas, but it wouldn't do that to the belly. I can't think of any other single morphs that cause a black belly pattern, but maybe I'm forgetting something.