Green is very tricky indeed. I have learned to shade it with a complimenting blue, or yellow, depending on the look you are going for.

Glowing green would be shaded with a subtle yellow, while a dark muted green skin would be shaded with a navy blue-ish color (adjusting opacity)

It's like shading yellow skins, you have to use orange for the darker areas, to make it look right. (again, adjusting opacity of the orange) I hope this helps ♥

Can't wait to see the update on your last skin post, you are very close to perfection with that one! :)