Why are autumn leaves mostly yellow in Europe and red in North America?

Evolution provides the answer - or, rather, a whole lot of intriguing answers

The stunning display of autumn is almost over - a few tattered yellow and russet leaves still cling to almost bare branches. I've loved these last few weeks, getting out into the woods to soak my retinae in the reds, oranges and yellows against lingering green. With all that wealth of colour at my feet as well, it's impossible not to come home with leaves stuffed in pockets. Some of them will be laminated and turned into bookmarks or mobiles. Musing on variation within a leaf, I found one miniature escutcheon emblazoned with a broad V-shaped stripe of yellow and orange, on a green background. I thought I'd never seen anything like it before, but having found one I started to find more and more.

Most likely, then, I've seen these patterned leaves many times before, without seeing them.