Hello, there isn't a white flower in the background, what you must be referring to is the light gray foliage plant, it is Teucrium fruticans 'Asureum' (Bush Germander) and has small blue/purple flowers when in bloom.

Thank You so much! I was guessing Artemesia alba. It is lovely with the fountain grass and lavender. I live in 10a coastal zone South west Florida. To duplicate your planting (I have a lovely rock,but no hillside), I would have to plant Pink Mulhy grass and blue sage. I'll have to research the Asurem for planting here. I'm a Master Gardener for Florida and love to help people solve problems in their yards. I'm not a designer like you so I like to follow professional designs to find examples for problem yards. Again, Thank You for posting your designs on Houzz and answering my question, Sherrill