Back to your original question re the green diamond, both natural and “coloured enhanced” diamonds are subject to irradiation to produce the colour. That’s why it can be difficult even for the GIA to differentiate between natural and enhanced. I believe that if they can’t tell, they decline to declare either way.
If you are planning to sell the diamond a GIA report will help with the sale.
I have been buying on eBay for over 15 years and have “scored” a number of times but it’s more luck than my talent. It’s definitely worth your while, if you have time and patience, to sift through listings. Sometimes people are lazy, sometimes people are mistaken so opportunities do come up.
Just don’t overspend and be prepared to be wrong on occasion. As I’ve discovered, not all things ”hallmarked” are in fact solid / real.
Enjoy your new hobby.
And as to color, yes, I researched a lot about green diamonds. Hoping someone here could help me and mentioned flourescence because I've seen very few diamonds glow like vasaline glass in my research of UV light and diamonds. Figured someone on here might have a natural green diamond with same UV glow or not. Since Diamonds turn green over a very long time exposed to radiation I was hoping that because mine glows like uranium glass it was also colored by uranium, same color. Also the hallmark on the ring is gem orianted, so when I bought it I assumed they placed top notch gems in settings. Still looking into maker but can't take clear picture of it.