Crunchy Leaves

While sitting outside during snack M looked up at the tree branches above us and noticed something about the leaves. 

"Some of them are still green and others are red."

Everyone looked at one another and shrugged their shoulders.

"I don't know."

"Well, I think maybe because like the leaves turn red when they hit the ground."

M looked back up at the branches.

"Oh, never mind. Some of the leaves are still red on the tree."

M thought for a moment and it was as if a light bulb went off in his head.

"Maybe they turn red and orange when they are ready to fall!"

The others nodded in agreement and seemed to like the explanation M gave. 

L noticed the leaves on the ground and crunched one in his fist. 

"The leaves are crunchy. They broke!"

M picked up a leaf and tried the same thing. 

"They crumble when you can crunch them."

The boys immediately began looking around in the areas surrounding them looking for crunchy leaves. 

F picked up a few and started crunching them between his fingers. 

"Look look this one is crunchy!"

Why were some of the leaves that fell crunchy and why were some still soft? 

"I think that they get crunchy when they turn brown like this one. I don't know why some leaves are red and crunchy."

By the end of our short conversation the boys decided that brown leaves are the crunchiest, leaves are ready to fall when they turn colors, and that not all leaves have to be crunchy. 

Why do leaves change color in the fall? Why are only some leaves on the tree still green?