About Light & Plants

Plants absorb red and blue light to make food (photosynthesis)
Plants don't need green light to make food, so it is reflected -- which is why plants are green! 
The primary colors of visible light are red, blue, and green. When combined in various amounts, 
these three colors can produce most colors.

Plants that are stressed or unhealthy don't make as much food,
so they reflect more red and blue light.
For unhealthy plants, they not only reflect the green wavelengths that healthy plants do, but they reflect some red and blue light as well