Shade plants offer much more color and variety than most of us imagine. Your best bet is to stick with plants that note full or part shade. We find good definitions to be 0-2 hours of sun for shade and 2-4 for part shade, and like some light and bright tones to punctuate shade.
Almost all spring bulbs work in areas around trees, since they will bloom before the tree leafs out.
For lots of color in shade plants through the season, consider bright annual Impatiens. They’re especially great in two or three rows to create a vivid band of color on the front border. Begonias love shade, too.