French ALIA AP with black coating

For a while I have had an old photo from an April 1982 article on THV ammo from the Belgian magazine AMI which has confused me. It shows a plastic MTM wallet of cartridges near the end of the article which was apparently a gift from André Antoine (THV / Alia inventor) to whomever the recipient was, and it was meant for testing, or as a gift. The box shows some Alia cartridges and a couple of them have a black colored projectile. As it happens, at SLICS a couple weeks ago I picked up a couple .357mag Alia cartridges with a similar black oxide coating and I am wondering if anybody knows about the history of these, or what the story on the coating is?

Photo from 1982 AMI magazine article:

Lineup of Alia cartridges: