What is happening with my acer?

My acer is not turning red most of the underside is still quite green. Can anyone give me an explanation?

Dear Tigerofbengala, congratulations, because I see your colaboration is growing after your last arriving.

About your question I say: Do you know what variety of Acer you have? The green colour is due to chlorophyll wich makes the food for the tree in the summer. If the leaves are still green, it means the plant is still able to make its food from sunlight. It is still relatively warm in your area? It could just be too early to go completely dormant and that the plant is trying to make all the food it can before winter.