I thought it was simple: While I’m sleeping, this spirit— something between Jack Flash and Jack Black — paints fall colors on the leaves when it starts to get colder and the nights get longer.
Turns out that it’s a bit more complicated and, if you like chemistry more than myth, a bit more interesting
Trees, the kind whose leaves change color in the fall, produce green chlorophyll in their leaves to photosynthesize sunlight, water, minerals and carbon dioxide into sugars which they live on.
When the nights get longer and days cooler, trees make less and less green chlorophyll and different chemical pigments become more prominent in different trees or at different stages of leaves turning-- reds, oranges, browns — as the sap leaves the trees, go down the twigs and trunk and are held in the roots until spring.
That might account for how the leaves change colors but how do you think the frost gets dusted on the garden in the early morning this time of year?