Green Tea falls in that same gray area as "non alcoholic" beers. It's not explicitly forbidden but do not be surprised if you lose your temple recommend over drinking it either.  
 
Any product that is brewed from tea leafs whether black or green tea leafs is a Hot Drink by definition. I know that many state that the antioxidants in Green Tea is good for you, but those same antioxidants can also be found in grape juice which doesn't have the drugs and acids that are harmful to your body like Green Tea does.  
 
I would recommend some grape juice for your antioxidants and to all together avoid any appearance of sin with Green Tea. It will protect your standing in the Church, as well as prevent you from consuming a beverage that is not good for your health.