Actually, According to the pokemon game research, it says that eventhough the pokemon are caught in the Johto Apricorn balls, the Johto balls will appear as regular pokeballs on platinum, Diamond, and Pearl. However, even if they do appear as regular pokeballs, they are still apricorn balls even if you traded the pokemon back and forth from Plat/D/P to HG/SS or HG/SS to Platinum/D/P. So they will only appear as the apricorn Johto balls if they're on HG/SS. :)