Reddish-orange leaves on boxwood like this in late winter can be associated with winter burn, drought stress, or low leaf nitrogen. We'd certainly rule out drought stress! Take a look at the information about winter injury in our publication about boxwood care. http://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/TreesandShrubs/...
Boxwoods require good drainage, ample amounts of organic matter, and grow best within a soil pH range of 6.5 to 7.2. You may want to have your soil tested if you haven't done so within the last three years to check your pH. https://extension.umd.edu/hgic/topics/soil-testing