GREEN          :

               The COLOUR of chlorophyll, the substance

               responsible for photosynthesis, with which

               GREEN plants are able to turn sheer SUN light

               (AND some AIR, WATER AND other stuff) into FOOD

               AND ENERGY. Curiously the spectrum of the SUN

               has a peak in GREEN (in other words it provides

               rather more GREEN light than blue OR RED).

               :

               A GREEN light being ON could mean Please_Edit