Green Balrog? Always thought of it as made of fire, ash and smoke... hmm hard to represent in plastic and paint so under those circumstances your version works fine :D
You could say this is the eco-friendly version with it being green
I think it works well in green to be honest, when i did my white metal jobbie i painted it grey with orange, red and yellow highlights, where the grey showed through i used bi-carb to simulate the ash and cinders on the skin.