Autumn leaves don't turn yellow. The yellow was there all summer

Autumn leaves don't really turn yellow. The yellow carotenoids were in the leaf all summer, hidden under green chlorophyll. In autumn the tree dismantles its solar panels to reclaim the nutrients inside, on average about 62% of a leaf's nitrogen, and the green drains away.

Red is different: many trees make it fresh, from sugar trapped in the leaf, and it glows brightest after sunny days and cool nights. Grow your own autumn and see what the weather does to it.