I can't imagine it would ever come up, but can you use the treebeard ally to play entmoot without a color match? I'm leaning yes, but I get these wrong sometimes.

Good question. I would say no, you can't do that. Treebeard says you can use his resources to pay for Ent cards played from your hand, but in this case you aren't paying anything. You could argue that you are paying 0, but that argument didn't hold up for A Good Harvest...

Right, this question has come up with Elrond and Good Harvest before. 0 cost events always require a color match, even if you have the ability to pay for cards in that sphere.