If your fry are white/pink or yellowish-white, and the parents are Black Convicts, then I assume the parents carry the pink/white gene, hence some fry are coming out as white/pink. The white/pink fry will most likely be white/pink when fully grown, hence they will never get any black stripes. If the fry are greyish with black bars, then they are black convicts.
I just gave away 60 convict fry at 1 month old that were free swimming for 3 weeks only. All the ones I gave away were black---meaning they were grey with black spots on them at that size. Almost half the fry were white/pink. These were the ones that I kept. The parents are black, but the mother carries the marbled gene, since her father was a marbled convict, hence his daughter is producing some white/pink fry.
Make sense?
At 1 month, you should be able to identify them between white and black cons. You wont be able to distinguish sex until they are at least 3-4months or almost 1 inch.