Why do leaves have color?

As I understand the argument by those who oppose intelligent design, all the different qualities of plants and animals are due to evolution.

The leaves on the trees are green due to chlorophyll. When the cold weather hits and the leaves die, the chlorophyll is no longer there to turn the leaf green and we see the spectacular yellows, oranges and reds of autumn. While we love the beauty, our appreciation does not qualify as a sufficient reason for the evolution of the trees.

How are these different colors supposed to benefit the trees?