And Peltier oxblood can differ a bit from Akro's. Like Chad said, I've seen it mostly on MCSs but I have seen it on a few others too.
It's a nice Rainbo though, no two ways about that.
The only Akro "Opal" I can think of is a Fire Opal and this isn't one of them. Akro Corkscrews on an off white UV reactive base are not too uncommon. And I think what you have there would be called "lazy corkscrews" as opposed to patches. But more views might alter my thinking on that.
The marbles shown in the article remind me a little of the Svenska Stenkulors but they appear have a final glaze or treatment of some sort. Yours don't look quite as glossy.
Very cool, Fire!
Here's an interesting little article about them. You may need to translate from french. Apparently the company opened in 1998.
https://forum.trictrac.net/t/article-billes-traditions-la-vraie-bille-en-terre/195137