That's a tricky one.
I could see it maybe having come from an Ace run but one with little white. Might need some of the white in there to get the opalescence. Have you seen the Peerless peewees which almost have a clear base ... just a wisp of white? [Very late edit: I'm pretty sure I would have meant to say Acme Realers there, rather than Peerless Patches.]
Since we don't see Aces identified very often, I've often wondered how short the production time was, and if it was short then why that might have been so. And one of my guesses was that it was hard to control the consistency of the Ace base.