Why do autumn leaves change their color?
1. https://www.esf.edu/pubprog/brochure/leaves/leaves.htm https://askabiologist.asu.edu/questions/why-do-leaves-change-color
The short answer is that chlorophyll breaks down, but it's actually more complicated.
When the chlorophyll breaks down, and the green color disappears and the yellow and orange colors show. Other chemical changes occur, making the more intricate colors.
The other things that affect the leaves colors are the weather, light and water supply.
The reason leaves are green not during Fall/Autumn is because the chlorophyll, that covers the leaf, are still there.
The reason chlorophyll breaks down during Fall/Autumn is because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process
The pigment that actually makes the leaves change color are the pigment "Carotenoids". Which becomes the main color of the leaf because the green pigment (chlorophyll) breaks down.