Fall in Florida is the season of purples. Asters, muhly, beautyberry - so many of fall's fantastic showstoppers here are purple. Another great example is Mexican Sage (Salvia leucantha), which begins blooming in early fall and lasts until first frost.
Though not native to Florida (it hails from Central American and Mexico), Mexican Sage is well-suited to our climate and shows no invasive tendencies. It has silvery green foliage that grows into almost shrub-like proportions by the end of summer (3 feet high and tall), when the flower stalks emerge and add another foot or so to the height. (Ours are still small - we planted them only a month or so ago when we got a great deal on the clearance rack at Lowe's.)
The stalks and calyxes are purple and fuzzy, while the blooms themselves are a soft white color. This late-bloomer is a favorite of pollinators like bees and butterflies, and is very easy to maintain. After the first flush of blooms has finished, cut back to the base (you'll see the new growth beneath) for continued blooming as long as the season permits.
Mexican Sage will likely die back to the ground if we have a hard frost, but will re-grow quickly once warmer weather arrives. We always love adding new salvia species to the butterfly garden in My Florida Backyard - especially those that add to the purple pageant of autumn!