Burnt glass is a thing, glass never melts together and mixes color wise.
Glass does not always get along with each other--hence the name " Experimental”--the true ones, not just the ones that were dug or rejected.
The glass colors may overpower one another making it look like it is mixed--kinda like a slag with no white showing--they just look different.
I believe that yours is a Popeye, Blue, Yellow and White.(white is always a color to me)
It just got too hot and the yellow turned grey.
Now, with a lack of yellow in one such as yours, it may explain the black shown in some Popeyes--they are very rare.
Popeyes are three colors--two from the "rainbow" and white--clear is not a color--just a base.
A hybrid would include 4 distinct colors.
Given that there are some color combos of "Popeyes" that show up more often than the rest as Hybrids.I wonder why?
Marble—On!!