We live on green patches in an otherwise blue planet. While green is certainly the foliar backdrop of the planet’s living skin, the land is bedazzled with every color of the rainbow, and then some. And then some because the rainbow only contains a small selection of colors; many colors are mixes of other colors; brown is a mix of red, yellow, and blue while pink is a blend of red and violet). The colors we see on leaves – greens, reds, yellows, purples – frequently represent adaptations that plants have for living well in place. Here we discover the reasons behind the many colors of plants, particularly in the fall.
Lets first start with light itself. The sun emits a broad spectrum of wavelengths, though not in equal concentrations, that continuously bombards our planet. Emissions peak in the visible spectrum, so we receive more blue light, which is towards the center of the visible spectrum, than violet. The higher energy shorter wavelengths of the cool end of the spectrum (indigos, and violets, see image below) are more likely to strike a particle of dirt, droplet of water, spore of fungus, etc. and be scattered in the atmosphere. We then see the sky as blue. When the sun is lower in the sky, light has to travel through more of the atmosphere before reaching us. A higher concentration of longer wavelength light (reds, oranges) is scattered, particularly when there are more particles in the air, and we get beautiful sunsets.