The Fall color thing is pretty simple, right. How many savvy "nature" enthusiast and experts have you had assure you that it depends on the rainfall, abundance or lack of,  during the summer or fall. Or that soil minerals are the determining factor. Or maybe some other phenomena of the universe, like man-made global warming or such.
  Below are two Sweet Gums I've observed over 20 years. They have made me question my belief in the "Sages" of things natural.
  Every Summer these gum's leaves are green. Every Fall they are more or less like the pictures below.  Every year.
  I've finally reached a logical conclusion about this matter - see below
What is surprising is their location, I'll bet you think environmentally different, right.  Wrong!
So believe what you see, not everything the experts tell you.

Conclusion - I don't have the anwser, I'm just a Monitor.