There are popular and scientific myths about the causes of fall colour in trees. Jack Frost is alleged to paint tree leaves with his chilling touch, bringing on colour change along with a frosty coating. Another twist on this myth is that Jack Frost brings reds and purples to autumn trees by pinching the leaves with his icy fingers. A less poetic explanation of fall colour, favoured by scientists for decades, is that the autumnal colouring of leaves was caused by waste products accumulated in the leaves and revealed to us with the fading of green chlorophyll pigments. As it turns out, the waste product theory now seems to be considered a bunch of, well, crud. The fall colour pigments are produced, or revealed, only in living leaf cells of deciduous trees during the critical, seasonal process of leaf senescence. In fact, if Jack Frost did his thing too early, or, in other words, if there was an early killing frost, the leaf colour display would be dulled, if not stopped altogether.
- Info from Why Tree Leaves turn color in Autumn