If you take this picture to a reputable nursery in your area, the people there can recommend what will work for you.

I would say consider shape as well as color. If your shrubs are more rounded, you should probably look at perennials with a different shape for the colored bits in between, or it'll look like a collection of orbs. Be aware that the magnolia, lilac, and the more common dwarf mugos will get pretty large over time. Arboretums and botanical gardens are great places to see how different plants fit together in a garden and get ideas. They often have signs with the names of the plants. I take pictures when I go and look up the plants I like when I get home.

There is aLandscape Design Form, I'd ask there.

tj