First thing that comes to mind are coleus, the ones that will take sun to part shade. They would give you plenty of color and foliage all you would have to do is keep the blooms pinched off.
here are some other possibilities:
Aconitum henryi 'Sparks Variety' Monkshood this gets up to 6 feet tall when staked otherwise it vines. So on a trellis it would look fantastic I think and the dark blue is a nice color I think. Blooms late summer. There are many species of monkshood that you can look at as possibilities for your garden.
Actaea pachypoda, Dolls Eyes blooms in
spring and has 3 season interest. But it is toxic so not good to have if you have children or pets.
Agapanthus 'Africanus'
lily-of-the-Nile I think this might go well with your iris.
Alstroemeria 'Mauve Majesty' Peruvian
lily These will bloom all summer long.
Amaryllis belladonna, Naked Lady These bloom in late summer after their foliage has disappeared. Of course in your
zone you could grow most of the amaryllis and I think they are beautiful.
Amsonia 'Blue Ice' Blue Star
flower Might make a nice eging plant for your bed.
Anemanthele lessoniana, Pheasant's Tail Grass This might make a nice backdrop for your bed up against your house. I think the colors might work well together.
Angelica gigas, Angelica If you like plants that look alittle odd here is a biennial that is interesting.
Celosia is another annual that you might want to add to your bed. It comes in most of your hot colors and is a real stunner. It self
seeds if not dead headed and also makes for great dried
flower arrangements.
Aristolochia contorta, Dutchman's Pipe
Artemisia lud. 'Valerie Finnis', White Sage
Aruncus d. 'Child of Two Worlds', Goatsbeard another nice background plant for your bed
Astilbe a. 'Bridal Veil', False Spirea some false spirea can handle your
zone some cannot so you'll have to research which ones you like best carefully.