We have a deck that is semi-shaded most of the day.

Wax Begonias. Coleus. Lobelia.

shade annuals......new guniea impatience,non stop begonias,fushia,torenia,lobelia,rex begonia,begonia,

begonias, petunias most of the flowers in the stores have tags that tell you what is best for what kind of sun -

Begonias and impatiens

impatiens, fuschia, lobelia

I have a huge maple in my front yard and it gets very little sun. I hang Tuberous Begonias in bright colors, like yellow and orangey red and it really perks up the area. They also don't require dead heading to get more flowers, they plant does it by itself. They flowered from the day we got them until the first frost and didn't even get exceptionally leggy. I wouldn't get anything but plants that tolerate mostly shade to some sun. There really are quite a few out there that will bring color for you. Check out greenhouses, they really know their flowers, then go to the big box stores and check out the flowers you want at a more reasonable price. I always have good luck at Home Depot, they seem to take good care of their stock.