Your options will be determined by what is happening in the six feet of space between the pool and the ugly wall. That is currently unknown. You can post a picture in the comments.

As the contractor who installed your pool since he is the expert with intimiate knowledge of your property and land. He or she has a responsibly to assist you since you were his or her paid client. Hope you kind the answer.

Photos help immensely in our ability to help you. Nonetheless, your question is about what to plant on the retaining wall.

Salvia greggii (Autumn Sage) is a low growing evergreen shrub with red, pink, purple or white flowers that bloom spring to fall. It's hardy to zone 7.

Muhlenbergia capillaris (Gulf Muhly) is a grass hardy to -15º. It's drought tolerant as well as tolerant of extended wet periods. In Oct its seedheads are pink, and especially brilliant with the sun behind them. It grows 2-3 feet high and wide. It's a warm season grass, so it does go dormant during winter.

Agastache rupestris (Red Hysop) is a perennial, hardy zones 4-9 with orange, apricot or red flowers through summer. It grows 3-5 ft. tall. It prefers lean, slightly acid, well drained soil. It goes dormant in winter and prefers not to be watered then.

All of the above plants are drought tolerant and prefer well drained soil and full sun. You should provide regular deep watering the first year after planting during dry spells, but this is true for any plant. They are also deer resistant. When landscaping it is best to mix several types of plants in groups. I would suggest you plant the Salvia and the Muhlenbergia at the top of the retaining wall and put the Agastache behind that. Only the Agastache needs cutting back after winter. The Muhlenbergia can have its old foliage trimmed back in spring when new foliage starts to grow but its not required.