Right. That does make sense. But how would that get implemented in a way that it can be used on the white ledger without exposing the source being block ledger "coin?"

I'm guessing that, if they use a black ledger, they will want a method to print infinite black coins that can be used on the white coin ledger. But that would have to be evident somehow in the code for the black coins. There's only so much they can hide if they need to interoperate.