Euphorbia 'Jade Dragon''-is an evergreen perennial with red-purple leaves in the spring that gradually turn blue-green as they mature. Plus, this colorful plant sends up huge, chartreuse flower heads in mid to late summer. It's deer-resistant, too!
Sea holly (Eryngium alpinum) has a wonderful, steely-blue color, intriguing spiky foliage, and a seriously tough nature. I had to have this in my garden after seeing it in large flowerbeds in Switzerland --- really beautiful!