From what I can tell the easiest way to tell the Green Gargoyle apart from the Slate Blue is the Green Gargoyle will have the phrase "USBC*" on a line between the serial number and the Made in the USA line.  Like many older balls blue seems to fade to green over time on these Gargoyles so going just by color of often crappy internet pics is asking for trouble.  Let me know if this is not true.  Examples below (pics taken over a decade ago so color was still obvious back then)  Thanks.

Green -

Blue -