Grass looks green because of the presence of a chemical called chlorophyll. This chemical works to convert the energy from the sun into food for grass.
Light from the sun is stored and then converted into sugar after chemical reactions have occurred within the grass. This process is known as photosynthesis, which uses water and carbon dioxide and produces oxygen.
Grass is green because of how the light reflects off it. It stores red and blue light, while yellow and green light bounce off, and that is what can be seen. Chlorophyll does not even touch a great deal of the light that comes from the sun, but it is an efficient storage and transferring part of the plant.