Is it part or full shade? I've had blue lobelia in the past that the stick in the container said full sun, but they did horrible and eventually died out completely by the end of July. I've read at other sites that partial shade is best for them, and they are very nice looking. Also check out Browallia (amethyst flower, bush violet), those should do well in shade.
Oh, and my preferred impatiens color is pink, or the cherry splash variety, but I usually end up with red to try and entice hummingbirds.
