Sieve Effect

 Leaves usually display a uniform color across the whole leaf. The pigmentation of the leaf is caused by the chlorophyll. The chlorophyll is what absorbs the light energy for photosynthesis. As can be seen by the leaf, the pigmentation is found throughout the leaf, covering as much area as possible. This is due to the sieve effect. The higher the concentration of pigmentation, the more light that is absorbed. However, if the leaf concentrates more pigment into one area, it lowers pigmentation in another area. By lowering pigmentation elsewhere, the leaf actually absorbs less light than if it had a uniform concentration throughout. This is why leaves are a consistent color across the whole leaf.