Cool Rainbo, Art. I've always liked the white in transparent ones - like slags with a more predictable structure. And the base on this one is great - I've seen it too, sort of a dark amber/red color. MMmmm good!
Maybe because it's a Pelt? š Nice lazy "S" on that seam in the 3rd pic.
If it's not Pelt, I'd have to go with an even weirder Marble King. I don't see Vitro no matter how I slice it.
Take a look at the second pic . . . see how that fat purple ribbon is actually two ribbons that originate on opposite sides of the seams? The bottom half of the ribbon in that view should be pulled out away from the top half and into all the wispy ones. Then it would look more like you'd expect for a 4-ribbon Rainbo - I'm sticking with Pelt.
Here is some info and other examples from peltiermarbles.info . . .
Superboy - Light blue base, red and yellow ribbons---usually the red lies on top of the yellow.
It seems there is a lot of variation in in "Superboys" . . .
A Superboy is basically a Superman without separate yellow ribbons. The red is usually found on top of the yellow in the same ribbons (looks orange), on a light blue base.