If you want lots of color in the shade then look to annual flowers like impatiens, lobelia and begonias. These are plants that bloom all summer until frost but need to be replaced each spring. If you were thinking of something more permanent like perennial plants that go dormant in the winter but return each spring than consider the tall blue spires of monkshood, the white blooms of Japanese anemone and the early blooming perennials like bleeding heart and saxifrage. There are so many different perennials that bloom at different times of the year that it really is like figuring out a jig saw puzzle to devise a plan so that something is in bloom throughout the growing season. If you would like to send me more details - the size of the bed and your climate and if you want annuals or perennials or even shrubs than I can help you with a more detailed plant. Winter is great time for garden scheming and dreaming.