Another good patio plant is Bougainvillea if you don't mind it's long thorns. It's available in purple, reed, rose, pink, orange, apricot, a yellow (i think) and white, so you can work in a favorite color. Very hard and low water (again I think).
Also the color and size of pavers here would be beautiful on that platform. The sides could be the same tile, or a colorful patterned tile to set off the edge and the step