Depends on the amount of light/number of trees in the area.
"There is a great variety of lesser vegetation found in association with loblolly pine. Some common understory trees and shrubs include flowering dogwood (Cornus florida), American holly (Ilex opaca), inkberry (I. glabra), yaupon (I. vomitoria), hawthorn (Crataegus spp.), southern bayberry (Myrica cerifera), pepperbush (Clethra spp.), sumac (Rhus spp.), and a number of ericaceous shrubs. Some common herbaceous species include bluestems (Andropogon spp.), panicums (Panicum spp.), sedges (Carex spp. and Cyperus spp.), and fennels (Eupatorium spp.)."
If the shade is not too dense, perhaps azaleas, coleus, indigofera
Hi. Here are some links offering flowering shade perennials. I do not know anything about the companies, but you can surely find many of them locally. Also, azaleas and hostas and Heucheras bring color to shady areas