"according to ackerman, exactly what causes leaves to change color? what particular conditions cause the brightest colors in autumn leaves? "

When the trees prepare to face the winter the leaves stop making chlorophyll and the colors that were hidden from sight during the spring and summer came to live. The climate is responsible for the most intense colors. In years when the fall sunlight is strongest and the nights are cold and dry, the leaves show their most intense colors

After the summer solstice, daylight gradually begins to shorten. Trees consider this and pull nutrients from their leaves back to their trunk and roots. This effectively chokes off any nourishment to the leaves and leaves them scarred and unable to produce chlorophyll. This scarring and lack of chlorophyll causes the leaves to change colors and eventually they will break down and fall off the tree.

The higher you go up the less oxygen there is