The bushes are growing beautifully but not turning color. They grow in partial sun in a well drained area.
My Burning Bush Isn’t Turning Red
Certified GKH Gardening Expert
Applying a fertilizer in the spring can help with boosting growth and overall appearance in the season.
Temperatures and changing light conditions affect the plant, there is likely nothing to be done except have patience!
Here is a link with growing information.