While impatiens are indeed shade loving, they are slow to establish in Cheyenne mostly because they abhor wind and cool nights. They do best in protected locations and even then don't start looking full until late July or early August. A favorite of mine that does well in light shade is the pansy . While they are often treated as an perennial they are best treated as an annual, planted every year. Snapdragons can also tolerate light shade.
Begonias always can tolerate shade well in Cheyenne.
There are some excellent choices for perennials in the shade . One of my favorites is Bleeding heart has fascinating flowers that live up to their name but only bloom for a few weeks. Delphinums with their tall blue spikes can tolerate a fair amount of shade. Columbine grows well in shade but blooms best if it gets a little sun during the day. Vinca grows in a viney fashion with glossy green leaves with a blue flower appearing in spring.