The fall colors aren't one thing. The yellow is old; the red is new.

Carotenoids (the yellows, the oranges) sit in the leaf all summer. Chlorophyll's green just drowns them out. When it breaks down, they show: the yellow was always there, masked.

The reds are different. Anthocyanins are built fresh in autumn, from sugar the tree spends, pigment made for leaves it is about to drop. Why it pays that cost is still argued.

So half the show was hidden all along, and half was made on purpose.