Ask Mr. Smarty Plants

For colorful flowering plants that grow in the shade I can give you a long list or you can look for them yourself by doing a COMBINATION SEARCH in our Native Plant Database and choosing "Louisisana" from the Select State or Province option, "Herb" or "Shrub" from the Habit (general appearance) and "Shade - Less than 2 hours of sun per day" under Light requirement.  There are other criteria you can choose as well.  Here are some representative plants from a search the criteria above and "Herb" under Habit (general appearance).  :

Coreopsis lanceolata (Lanceleaf coreopsis)

Iris brevicaulis (Zigzag iris)

Lobelia cardinalis (Cardinal flower)

Oenothera biennis (Common evening-primrose)

Packera obovata (Golden groundsel)

Phlox divaricata (Wild blue phlox)

Ruellia nudiflora (Violet ruellia)

Rudbeckia hirta (Black-eyed susan)

Salvia coccinea (Scarlet sage)

Salvia lyrata (Lyreleaf sage)

Solidago altissima (Tall goldenrod)

Viola missouriensis (Missouri violet)

There are many more possibilities.

There may be a problem growing plants under your oak tree, not just because it will be shady but because the oak tree has an allelopathic effect on some other plants.  Allelopathy is a situation where a plant releases a chemical that has an effect on another plant.  The effect may be beneficial or harmful, but the ones we hear about the most are those that are harmful to another plant.  One of best known of the allelopathic plants is the walnut tree (Juglans spp.).  It has a very strong effect on most plants attempting to grow beneath it.  Trees with a lesser allelopathic effect include oaks, hackberries and eucalyptus trees.  Red oaks, which in your area would probably be Quercus falcata (Southern red oak) are mentioned more often than other oak trees.  You can read more about allelopathy in this article, Allelopathic plants: nature's weedkillers.  That said, not all plants are susceptible to the oak's chemicals.  Some plants can grow under oaks.  Unfortunately, there are no lists of plants that will grow under oaks although you can find lists of ones that will grow under the allelopathic walnut trees.  Since live oaks don't appear as large threats as allelopathic sources, your challenge will probably be getting plants that will do well in the shade.  Those above should all do well in the shade.