I'd recommend the Germander or Santolina over the Cerastium, which tends not to be long lived and needs frequent replacing over time. Lower growing Lavenders such as Lavandula stoechas are probably best if you don't want anything or 2.5 feet tall. You might also consider ground covers such as Myoporum parvifolium 'Dwarf Pink Form'. or one of the gray leafed and red flowering Zauschneria cultivars. Tulbahia violacea or T. v. 'Silver Lace' could also look good under olives. Calamintha is another easy to grow and nearly everblooming drought tolerant low groundcover.
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lavandula stoechas
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