Oh noooooo! I did it AGAIN! Hit the wrong key and the Apple ate my post. Grrrr. I AM an idiot.
OK, here's the short version:
Dovesgate, I LOVE chrysoberyl. Congratulations on your purchase. Is your ring newly fashioned or vintage?
No doubt, you know this: chrysoberyl is pleochroic, meaning that the gem shows two or more colors, depending upon which angle you view the stone (actually, chrysoberyl shows three different colors). And, of course, "ordinary" chrysoberyl that shows color-change (specifically, it displays different colors in different lighting sources) is known as the "extraordinary" variety of chrysoberyl called alexandrite. Interesting that you have a gem identified as chrysoberyl that shows the more rare, coveted (and expensive) charactersitic of alexandrite. What color is your gem in daylight? Incandescent light?
Personally, I have no direct experience with AGL, although I know several gem cutters and dealers who respect the lab. I am sure they, and OMC, know best. That being said, I'd wager a guess that no US lab has more resources at their disposal than GIA... if you need them (and don't mind paying the price). For what it is worth, I think magnification is the only way to distinguish natural chrysoberyl from manmade. Also, a lab will be able to identify the specific chemical properties of your gem.
I hope we get to see a pic of your new ring one of these days!