Maple Tree · Gardenality Genius · Zone 10A · 30° to 35° F
Hi Deb-Hearing your Lemon Ball Sedum is turning white makes me believe it has a fungal disease. Heavy frost, root rot, crown rot, over fertilization, or possibly coming in contact with herbicides would most likely turn leaves yellow, brown or black before dying. The most prevelant diseases are fungal diseases on sedums. Mold and powdery mildews will leave a powdery grey to white substance on leaves and stems. These diseases are normally caused by too wet a soil, poor drainage, too little sun, poor air circulation, and or overhead watering that is allowed to stay and not dry over a short period of time. Sedum prefers bright direct sunlight that is intense enough to keep the soil and foliage sufficiently dry to deprive fungi from developing.
Is the soil well draining? Is the soil more on the dry side or is it wet most of the time? Has your location had a lot of rainfall keeping the soil wet not allowing any drying of the soil in the last few months? Are the leaves actually turning white or white spots that grow with time eventually turning the whole leaf's color? Does the white coloring look as though it is a powdery or fine growth that may be covering the leaves?
If you could answer these questions and upload a close up picture of the plant it would help in identifying the problem. Above this and to the right of your name below your question you will see where you can upload any pictures you have in a file on your computer.

Gardenality.com · Gardenality Genius · Zone 8A · 10° to 15° F
John could be right about a fungal disease. I had this problemwith ice plant. It was a sticky, gooey white substance that formed on the foliage during a period of wet weather. The plants never recovered. If the leaves are simply turning white, it could be frost damage, a nutrient issue or some other condition. As John mentioned, a closeup picture would be helpful for a proper diagnosis and possible remedy.