My appetite for 'floating colors' remains a strong value to me that autumn allows to fully enjoy.
Beside the large amount of strong colors displayed in autumn, what strikes me is the environment color tone. Others seasons environment lighting are mainly influenced by the sky, the cloud, the sun light tone but autumn have also stunning property of bringing a colorful environment lighting in natural environment which can be pretty sparse.
I really like graphics engine that features smooth day and night transitions more recently smooth weather transitions that physically based lighting allows. My guess is that the next step will be smooth season transitions... That would be nice isn't it?