If you have only had it since last autumn (which seems probable) you will have only seen it in it`s autmn colours, and the leaves you are seeing now are it`s new spring colours which will turn red again later in the year. What variety is it? Does it drop it`s leaves in the winter, or is it evergreen?What is your soil, acid or alkaline? These questions help with a diagnosis.
If it is a variety that should be red all of the time then it could be due to being in too much shade, lack of nutrients or poor soil. Which variety do you have?
The red colour takes time to build up in the leaves. They will be green when they first come out. It is the same with copper beech trees - always green to start with until the leaves have had time to mature.
Thanks guys, not sure of variety, the soil is acid, it has been transplanted about 5 years ago. not evergreen. It has two stems, the older carries the red leaves, the new is green,it seems healthy enough.