Agree with TS, a blue hosta would be perfect. We have 4 different hostas in shady areas of our back yard that love our NW climate. Every year they come back bigger and more beautiful that before. So many varigated leaf patterns to choose from too.
Also consider a small Rhododendren. Everyone in Oregon has the standard pinks, purples and reds, I myself am looking for one of the orange varieties. They are more delicate and would add great color and love the shade.
Happy Gardening!