Two of my favorites in this pic. Lamium 'Beacon Silver' and Chrysogonum virginianum 'Eco Lacquered Spider'. They both should be hardy in zone 6. They are evergreen here in zone 7a and the Lamium is a really good reseeder but not a thug. Both are excellent weed suppressors. The darker Ajuga is a great contrast to the silver Lamium foliage.