Our native Iris cristata, known as the dwarf crested iris, has flowers that range from white through violet. It spreads into colonies and has small sword-shaped leaves and grows in both sun and shade in zones 4 to 8 with May bloom.
Our native Jacob's Ladder (Polemonium reptans) also grows in both sun and shade as long as it has adequate moisture. Its lavender blooms appear in April.
Our native wild geranium (G.maculatum) blooms April through July in zones 3 to 8 and also produces pretty, little 5-petalled flowers in both sun and shade.
A larger plant in the same color family is the Great Blue Lobelia (L.siphilitica), which is a large clump-forming, 2-3 feet tall purple/blue flowering native that prefers medium to wet soil and some shade. It flowers July through October.
Liatris, also known as blazing star, is a magnet for monarch butterflies and produces stalks of purple blossoms in sunny locations August through September.
And in August through October the gorgeous dark-blue bottle gentian (Gentiana Andrewsii), which grows 2 feet high in sun to part sun, blooms, and those tightly closed blossoms are pollinated only by bumblebees. They are slow growing but long lived, and bumblebees are the only insects strong enough to open the closed bulbous blossoms.