Why do leaves change color?

You ask: Why leaf change color?

Leaf green come from tiny green stuff packed inside — Caveman call it green-catcher. Green-catcher grab sun light, mix it with water and air to make food for tree. All warm season the leaf full of it, so leaf look green. When days get short and cold, tree know winter near. Tree stop making green-catcher and break it down, pulling about half the leaf's good bits back into branch to save for spring. Green fade away. Now yellow and orange show — they hide in the leaf all along, just buried under the green! Some tree even make fresh red from trapped sugar. Then leaf let go and fall. Cave wisdom: leaf not turn color — green just leave, and hidden color finally get to show.