Blue zinger sedge grass could work and the blue tone would give some contrast to the green boxwood. I don’t know if you gave enough space, but I really like pancake arborvitae. It grows 1.5 feet tall by up to 3 feet wide. Lovely evergreen with a blue cast, soft to touch. Would need more sun than you might have now that I’m thinking about it though.

Take a look at Carex 'Feather Falls'--striped and evergreen, apparently good for sun and shade. Might get too large for you though. Another possibility, variegated Liriope--very handsome, but requires shade.

Thank you khan and laceyveil!!

Dorian, I’d sure look at Ogon Sweet Flag / Japanese Golden Sweet Flag. It’s listed as semi evergreen but in my yard it’s evergreen & we’re in same zone. Doesn’t spread fast & easy to control. The yellow & striped leaves are the perfect contrast to the green - exactly the reason I have it on a backyard slope. Link to search Sweet Flag

Thank you everyone. I am leaning toward the Liriope variegated. I love Acorus ogon and I have a large planting my a small stream in my backyard. Before I buy a large number of Liriope, my primary concern is whether it will look washed out.. I.e. too white. I have a dwarf hinoki cypress as a specimen at the very front.

Try a native carex. There are many different ones and you should be able to find one you like. Native is better than liriope.