How about some violas or mini pansys as some call them the purple ones really make the Heuchera stand out. Also Sweet woodruft as a ground cover.
Good luck

Japaneese painted ferns will grow in sun provided enough H2O. Or purple coneflowers, purple fountain grass or something gray like lamb's ear or powis castle artemisia.

maybe a smoke bush? they are one of my very favorite shrubs, and can be coaxed to grow side-to-side that than in a circle, which would make a nice backdrop.

Lysimachia is an option, if you can find it- chocolate/burgundy foliage make the yellow flowers a bonus, but not needed (I crown mine before they bloom, like I do with the lamb's ear)

there's also a standing artemesia whose name I never remember- 3 ft tall, upright habit, and a lovely silver/green color, perfect for the back of a sun bed :)

there are also some new 'bronze' heucheras coming out- but I'll wait until they aren't $25 a pot, y'know?