The arrival of autumn is a great reason to talk about chemistry: When tree leaves change from green to reds, oranges, yellows, and browns, we’re seeing the tree’s green chlorophyll fade away, revealing hidden autumnal pigments.he arrival of autumn is a great reason to talk about chemistry: When tree leaves change from green to reds, oranges, yellows, and browns, we’re seeing the tree’s green chlorophyll fade away, revealing hidden autumnal pigments.