Not so sure platinum is "just a leucistic or albino", platinum JD for example, a combo of two different genes. Gold (which I believe is leucistic?) and electric blue, but not "just a leucistic" by any means. Not sure I've ever heard of any platinum fish (or any other animal) that only carried one color morph gene, they're almost always a combo of genes.
Also not clear how an albino or leucistic fish could possibly have black fins as part & parcel of it's phenotype, albinism/leucisim should strip any such pigments completely. I have to think that an albino/leucistic fish displaying such traits, has been fed something which deposited this dark pigmentation...odd that such fish only show the dark coloration in their fins & not on the body.