It is sometimes challenging to think of combinations of plants that share similar characteristics — for example, bloom-time, sun or shade, drainage and amount of moisture. And if those aspects aren't challenging enough, many gardeners have to consider deer resistance as well.
One useful plant for a combination is catmint, which has grey foliage and lavender/blue blooms. Depending on the size of the planting area one might consider varieties such as the large clump-forming ‘Six Hills Giant' and the smaller variety ‘Walker's Low', though it is not really a short perennial despite its name.
Catmint can be combined with Russian sage, which is a similar color, in a hot sunny area where height is required and with salvia ‘May Night' for a harmonizing color scheme, since the salvia produces dark purple spires. Deadhead faithfully and you will stimulate recurring bloom.
If you want more blue, add veronica ‘Crater Lake Blue'. These plants are all drought tolerant once established and are deer resistant.
Then you can play with a few bright accent colors: yarrow ‘Moonshine', yellow black-eyed Susans, white shasta daisies, scarlet Crocrosmia ‘Lucifer', or Gaillardia ‘Fire Wheel'.
Bright accents will make the blue/grey background plantings pop!