purple petioles (leaf stems) happen with LED more times than not, so it's hard to use it as a symptom reliably.
REd streaks in stems indicates low sulfur, but could also just be genetics.
These leaves look overly lush, but could be turning purple, too. You'll have to watch for other symptoms to rule out possibilities.
Colder temperatures at night (68F and below) will exaggerate autumn colors, too.