Why is the Grass Green?

One of the kids at the elementary school where I volunteer asked me why grass is green.

Good question for a seven year old. I think I was at least sixteen before I thought to wonder about that.

Anyway, the answer has to do with pigments. Pigments are any substance that absorbs light. We have all seen rainbows so we know that sunlight is made up of many colors. The ones we can see run from red to violet with all the other visible light between those two. The frequency of light a pigment absorbs determines its color. What’s a bit confusing is that the color of the pigment is actually the color of light it doesn’t absorb. If the pigment looks red, then it has absorbed all the colors but red, which it reflects.

Plants have pigments which don’t absorb much green, which they reflect. So plants, including grass, look green.