According to the passage, why are most leaves green during the summer?

Every fall, many trees across the United States put on a show. Leaves that were green all summer turn yellow, orange, red, and even purple. Most people enjoy the colors, but few know what is actually happening inside each leaf.

A leaf is green because it contains chlorophyll. Chlorophyll is a substance that helps a plant use sunlight to make food from water and air. During the long, sunny days of spring and summer, leaves are so full of chlorophyll that its bright green color hides every other color in the leaf.

As fall arrives, the days grow shorter and the nights grow cooler. The tree begins to get ready for winter, and its leaves stop making new chlorophyll. As the green slowly fades, yellow and orange colors that were in the leaf all along begin to show through.

Red and purple work differently. In some trees, such as many maples, the leaves make new red coloring in the fall. Sunny days followed by cool nights that are not quite freezing help produce the brightest reds.

In much of Texas, fall stays warm for a long time, and many trees do not change color as brightly as trees farther north. But there are exceptions. At Lost Maples State Natural Area in the Texas Hill Country, bigtooth maple trees turn brilliant shades of red, orange, and gold, and visitors drive from all over the state to see them.

Soon after the colors appear, the leaves fall. The tree rests through the winter, and in spring it grows new green leaves. Then the cycle begins again.