You could do all grasses

Moraga Country Club Small Frontyard · More Info

Or?

Start with a focal point (here a boulder), fill in around it? Incidentally, I tried some "pops of color", preferred the quiet, almost Asian peace of this. But that's your call . . .

Why not to make it flat?

I’m with Celery. Is it mounded up for a specific reason? For instance, to help provide privacy? The mound seems to complicate this process unnecessarily.

Not mounded for a reason and the mound is slight. I think it was originally mounded because it was visually interesting and perhaps to keep water from pooling near the rock facing on the pool.

I would do a plain green groundcover to set off the pool. It's the elegant part of the scene. I wouldn't distract from it with busyness. Whatever dark green groundcover grows well in your area in sun.