<P> Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, various shades of red, yellow, purple, black, orange, pink, magenta, blue and brown . The phenomenon is commonly called autumn colours or autumn foliage in British English and fall colors, fall foliage or simply foliage in American English . </P> <P> In some areas of Canada and the United States, "leaf peeping" tourism is a major contribution to economic activity . This tourist activity occurs between the beginning of color changes and the onset of leaf fall, usually around September and October in the Northern Hemisphere and April to May in the Southern Hemisphere . </P> <P> A green leaf is green because of the presence of a pigment known as chlorophyll, which is inside an organelle called a chloroplast . When they are abundant in the leaf's cells, as they are during the growing season, the chlorophyll's green color dominates and masks out the colors of any other pigments that may be present in the leaf . Thus, the leaves of summer are characteristically green . </P>

When do trees change colors in the fall
find me the text answering this question