Question
My boxwood leaves are curling.  They are not turning yellow, although their color could be better.  Thank you for your help

Answer
Sounds like an insect called boxwood  psyllid ,Cacopsylla buxi. The boxwood psyllid is a small sucking insect that attacks tender young boxwood foliage as it emerges in spring. This stunts the growth of the shoots and causes the leaves to cup or curl and turn yellow. You may also find some white, waxy fibers around the curled leaves. Fortunately, this pest doesn't usually cause serious damage to the plant.

Control is to treat the boxwood with an insecticide. I would recommend that you use a systemic insecticide called Bayer Advanced Protect & Feed Granules. This is duel product of insecticide and fertilizer. It is applied to the soil under the shrub and watered in and the roots transport the insecticide to the foliage and when the insect sucks the plant juices it is killed. Check with your local nursery from this product.
Here is a web link to Bayer Advanced. http://www.bayeradvanced.com/product/Tree-Shrub-Protect-Feed/granule.html