Summer's so green...

...and winter's grey. Well, most places. The seasonal change in color is distinct (unless you live in the tropics).

It's so distinct that our brains actually adjust how we perceive color depending on the time of year. (The study was done at the University of York, my alma mater).

Of course, it's all to help us pick things out of a sea of green in summer, or spot that ice on the sidewalk in winter.

Needless to say this study was done in a temperate area. Presumably, humans who live in tropical Africa or India don't see, pun intended, any changes.