Hostas and ferns are two things to consider. Hostas come in all sizes, from the very large to the very petite. They also come in different shades of green and blue foliage with many variegated ones to "light up" a dark area.

For color, look into impatiens (sold as annuals) and epimediums (sold as perennials perhaps).

creeping jenny would look lovely hanging over any containers...a lovely light green color.

If you want some color, you could try a few containers with some bright spots, like gerbera daisy, and exchange the containers 1-2 times per week with those in a sunnier locale...I do this with my porch, which gets no sun at all, because I love the gerbera daisies....

There are vines that will grow in shade..maple, that give color come fall. Add begonias to the list of colorful annuals. Autumn and Japanese painted ferns give some color.
My other color giving perennials are zone specific and I am not sure about them in containers. Baneberry, Jack in the pulpit, etc.