I've got a very similar situation. I planted oakleaf Hydrangea (H. quercifolia) along my home and despite the shading canopy of the maple, they get terrific red fall color. Under the tree, I've got a huge bed--probably 25 by 15 feet--because it was so shady the grass was thin and the ground was bare. I planted a group of three Annabelle Hydrangeas (H. arborescens 'Annabelle') and scattered three Forever Pink Hydrangeas (H. macrophylla 'Forever Pink' around the bed. They've done exceptionally well--they filled in and give me color, but the bed looks a little bare in winter. I'm going to add a Yew (Taxus species) or three to solve that. Finally, because Sum and Substance is one of my favorite Hostas, I've got a serpentine planting of them through the bed. I dotted about three or four large green or green/blue Hostas (such as Abiqua Drinking Gourd) behind the Sum and Substance and some smaller ordinary green-and-white Hostas clustered in front. (They were from a friend's garden, so I don't know the name.) I've got daffodils and grape hyacinth for some early spring color before the tree leafs out, and I plant some annual impatiens in a drift in front for summer color. It sounds like a really ordinary planting because it's primarily Hydrangea and Hosta, but the combination of different sizes and colors makes the design dynamic and the simple addition of impatiens completes the picture.