Speak to me, my gardening friends, of your favorite shade perennials viable in Zone 4 (avg. annual lowest temp is -20 to -25 F, or -29 to -32 C). I'm in college for Horticulture, and our semester project for Perennials class is designing a planting plan for a huge woodlot area that's mostly part to full shade. I do not want to do the ordinary thing and use a ton of hostas. Bonus points if the plant has white/cream, blue/purple or yellow flowers, but I'm open to foliage plants and ferns and such as well.