Color and native and that size makes for a difficult question. Full sized crape myrtle varieties are all that but native. Native possibilities include desert willow, smoke tree (probably not large enough or spreading enough for your specifications), eve's necklace (Sophora affinis), Texas Mountain Laurel (very slow grower), and Texas redbud (not eastern redbud but rather Cercis canadensis var. texensis).
You can plant trees now if you are very careful to keep the roots moist but not soggy. This requires careful (not totally soaking the root zone) daily to every other day watering for a few weeks and then every other day to every 3-4 days for another month or so.
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