Tulips are a very colorful flower that can take full sun but they come up in the early spring and only last a week or so. So on to other possibilities.
Crocuses are another pretty flower that come in white, yellow, blue and purple.
Daffodils are another flower that would do well the area you are wanting to fill in.
Coleus is another pretty plant with very colorful and varigated leaves.
Impatiens come in a wide variety of colors and are prolific bloomers.
And to insure blooms into the fall try these Marigolds.
And to be different, try some Cabbages and Kale.
These give you a wide variety of flowers for in front of your porch. And I have never seen the Cabbages and Kale before. Im going to invest in some of those.