Colours of Nature

The pigment chlorophyll is familiar to us for coloring the leaves green. But how does it give green color to leaves might not be noticed by us.

The unabsorbed color of the light by an object determines its color. The acquired color of the matter is the complement color of the unabsorbed one from the light that passes through it. That is, anything that absorbs red light appears blue-green, and that absorbs green appears purple. When sunlight falls on leaves, the chlorophyll absorbs red and blue rays, diminishing their reflections, and hence the color green appears on leaves.

Another pigment called carotene is also present on leaves of many plants that absorbs blue-

green and blue rays and reflects yellow. The green and yellow pigments together give the leaves brighter green. While chlorophyll is an unstable compound, carotene is stable. Thus, when the former disappears, the latter turns the leaves yellow, making the leaf aged. Similarly, flowers and fruits get dipped in vibrant colors by many pigment molecules present in the cell sap. The cyanidin-based molecules anthocyanins and anthoxanthins give flowers blue and yellow color, respectively.

But sometimes, the same molecule for pigmentation can provide different colors to different species because there are other reasons for coloration. For instance, red rose and blue cornflower contain the same pigment molecules called cyaniding diglucoside, a kind of anthocyanin. The pH of the cell sap makes the pigmentation different as the cell sap of rose is acidic, whereas that of cornflower is alkaline. So never wonder when hydrangea flowers turn purple to bluish pink.

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