Several sprouted English box show branches with pale green leaves, while most of the plant is of normal color. These are about three or four years old. Is the decline dangerous to my older boxwood, or is it systemic within each plant?
At this point, prune out the branches with pale leaves and keep an eye on it. This should not spread.
Monitor the plants and if you continue to notice symptoms, you can send us photos of the whole shrub, around the base, and affected branches. Some possibilities may be root rot, voles, etc.
Here is our publication on boxwood and some information on pruning.