Acer - Leaf Problems
 

I have a large half standard acer in a stone pot. The leaves used be extremely bright green but over the last couple of years the leaves seem to be a lot duller.

I dont' think I am over watering it and I give it a feed once a year, is there any reason why the leaves would not be as bright as they used to be?

This is my first time on this site so thanks in advance for any advice.