Whats your location its not listed ?
I posted thread "Signs of Autumn "
Here many of mine doing the same displaying yellow and some with leaf drop afterwards, some with heavy rust thats expected just a few weeks earlier though - signs of autumn that im seeing here as the trees can sense less daylight hours as well as cooler nightime temps.
If your plant has been getting the needed moisture then yes signs of Autumn if not then signs of water needs but once leaves are yellow they will not turn back green.