Nepeta - probably Walker's Low which is popular and easy to find virtually anywhere plants are sold. Grey foliage with lavender blue flower spikes. Not fussy; takes whatever you can throw at it.

I like the idea of adding some purple color. I don't know if you're looking for shurbs or perennials, or a specific time of year for the blooms, or all season. Also your zone is a lot warmer then mine but some of the longer blooming purple perennials I have are salvia (sage), Catmint (nepeta), russian sage, obedient plant, lamb's ear, campanula glomerta (not carpatica - although that could work too), balloon flower (blooms only last a month or so for me), tall Phlox.
You could also add some yellow. I'd try to stay more lemony yellow then golden, but you could try oenthera (sun drops), coreposis, daylillies, yarrow, chrysthanthmums.

good luck!

Um, what color is your house and hardscape? Stumbling blindly here, I'll suggest gray foliage plants such as Artemisia Stelleriana, Salix Helvetica, or a juniper with blue-gray needles.

For gray foliage plants, let me add Lavandula intermedia 'White Grosso,' a gray foliage lavender with white flowers. In your climate, it will grow to small shrub size.

Mine are a year old; I doubt they will ever grow to their potential because of our winters, but who knows? Very happy with some morning shade, then full sun from late morning till the end of the day.