Question: why is the grass green?

Andrew Cairns answered on 13 Nov 2011:

Grass is green because it is the colour of light that plants need least.

Light from the sun is made up of all the colours of the rainbow – Red, Orange, Yellow, Green, Blue, Indigo and Violet. This goes in order of increasing energy – so blue, indigo and violet light has the most energy.

Plants absorb this energy to turn water and carbon dioxide into food to live through a process called photosynthesis, which requires specific high energy light. This happens in chlorophyl, so people often say that ‘plants are green because chlorophyl is green’. True, but the real reason is that the plant doesn’t need this light so it reflects it, and we therefore see it as green.