The general principal behind fall color change seems to be protect the most valuable first and the most expendable last. The top and tips of a tree are where the leaves have the most exposure to sunlight. As a result, these areas have the most capacity for future energy returns (in the form of photosynthesis). Rather than risking exposing these precious leaves to an early frost, fall comes earlier at the crown. On sugar maples (see image below), the tips are often bare while the mid-section is burnt orange and the bottom green. Similar for the edges of a leaf, the extremities are the areas most susceptible to cold temperatures and so the edge is also the first to change colors.
Left: Black locust leaf changing from tip towards the branch. Right: Cottonwood with bare tips at the top, yellow midsection, and green skirt (Centennial Woods, Burlington).
Left: Row of red x silver maple hybrids.
Center: Pair of sugar maples.
Right: Looking up at the red canopy of a red x silver maple, while the interior and lower branches are still red (Burlington)