With some plants the change of colour in autumn comes all at once throughout the plant, with some (my Parrotia, for instance, although leaf tips show first) more or less at random. I was just watching an Acer tschonoskii that is turning from the trunk out - all of the ends of the branches are still green while the leaves closer to the trunk are turning colour. Any plant physiologists out there that can make sense of this process and tell us why it varies so much?
I think the fall colour change is influenced by many environmental factors. The amount of rainfall the plant receives and other weather factors like temperature affect the production and breakdown of the chemicals that cause the pigmentation. Leaf colour is often most intense at the top of the tree, where sun exposure is greatest. Newer leaves may change more quickly or more slowly resulting in a more mottled look on the plant. There are many issues at play in this. Here is an interesting article about it from Davidsonia: http://www.davidsonia.org/files/14_4_guy_autumn_colours.pdf
Yes, we are in a pocket of good climatic conditions right on the Pacific Ocean influence in British Columbia. We haven't dropped below -5 C for a few years right where I am, and many plants can take that for a brief time. I get to grow things like Loropetalum and Rhododendron dalhousiae in the ground.
