Have you tried Drift Roses?
Popular with landscapers and designers since their introduction, Drift Roses add color to the garden in the heat of summer.
The small dark green foliage is similar to that of a miniature rose. Their smaller mature size is 2 x 2' and can be trimmed in early spring to maintain form if necessary. Drift Roses are a cold hardy groundcover useful for filling gaps in the front of the border. They really make a statement when used in large groupings.
These everblooming roses, flowering from spring until frost, are available at KAT Nurseries in ivory, pink, red, peach and coral in a #2 container.
Here's an article with more ideas for adding color to the summer landscape:
Summer Flowering Shrubs