Forest Flame has bright red new foliage in spring. This then fades to yellow and eventually turns green as teh season progresses.
It is an ericaceous plant which means it needs acid soil and soft water, preferably rain water. If you have planted it in alkaline soil it will struggle. If you've been watering it with hard tap water it will struggle as the alkalinity prevents it taking up certain nutrients from the soil and it will become anaemic.
If you do have it in neutral to acid soil and do not have hard water it will benefit from a good mulch of ericaceous compost for rhododendrons, azaleas and heathers.
If you soil is neutral to alkalin you need to transfer it to a pot filled with ericaceous compost and water it with an ericaceous feed which contains sequestered iron. The food available in teh compost will be used up within 6 weeks to 3 months so you will have to make sure it gets extra food and all its water needs. Never use hard tap water.
Here is some info from the RHS - http://apps.rhs.org.uk/plantselector/plant?plantid=1469