...Could be that the BB is an aquarium strain one and is therefore quite inbred, which means that the offsprings prolly have a lot of the same BB alleles, which makes them look very similar (because they do share heaps of similarity genetics-wise). FH would vary quite a bit, which is prolly the small bits of variations that one may notice in this case. Possibly...
Any fry from any strain of BBs would look very similar to one another...no matter the genetic diversity, or lack thereof. All pure species by definition are uniform in type. To put it simply, having one pure species parent means they will have 50% unscrambled genetics, hence the more uniform appearance. The slight differences were introduced by the mother, her genetic background is mixed species & therefore not set/stable.