well stomach color was just his indicator of food, since he had orange food otohime(bbs skipped) he could see when they had their bellys full of it. Silver was more the default, not necessarily because of rots but since they were not orange like the other this was the conclusion. Even in the presence of otohime feedings the fry that refused to morph never had an orange belly. once the rots were killed off they got orange bellies full of otohime and meta'ed. This was also a one time occurrence so yeah, in the wild NS would have weeded them out. But it's something to consider since off hand occurrences like this can sometimes reveal something. but anyway, where are those videos!