Colorful perennials that stand 4 to 6 feet tall include deep blue delphiniums and purple blue monkshood, foxgloves, rudbeckia daisy, canna tropicanna, (but canna bulbs may freeze in your area without winter protection) and white and pink flowering phlox. The volcano phlox is mildew resistant and comes in several colors. There are many more choices that will grow that tall depending on your soil and fertilizing habits. I suggest you visit a botanical garden in the area or university demo garden to get some great ideas on some unusual perennials for your area. Sounds like you will have a beautiful garden. Keep growing, Marianne Binetti