Want to see autumn colors in Jiuzhaigou while avoiding the crowds, what is the best time?

My wife and I would like to go there. I read many times that the best period would be in October but I'm quite surprise because I went in Chengdu & Qincheng mountains at mid-November this year and there were only a few trees with red or yellow color... So is there a big difference between Qincheng & Jiuzhaigou that could explain this?