There are some perennials that provide an added bonus of foliage that changes color in the fall.  For example, some species of Amsonia feature brilliant yellow foliage. The common name is blue stars, as the plants have pretty little blue flowers in the spring. Another, less poetic common name is dogbane.   The narrow leaves are lancelike, similar to the foliage of a willow, and the stems have a milky sap.  All Amsonias are native to North America and like full sun or partial shade and moist soil, but established plants can tolerate dry soils. Plants can be cut back after flowering to keep them compact as they can grow up to 4 feet in large clumps in zones 5 through 9. They can also be divided either in spring or fall.   Amsonia ciliata or Downy Blue Star, native to our southeast, is a good one for small gardens, as its clumps are only a foot wide. Because of its pale blue flowers, it combines well with other spring bloomers and when its elegant thin leaves turn yellow it provides impact in the fall garden, especially next to dark purple asters. This is a plant that pays its way by performing well across the seasons.