Photosynthesis occurs in all plant life and is responsible for making them green. Why are not all plant life green. I.e. flowers can be yellow, red and some leaves too like the leaves of Poinsettia. Is the reason because no photosynthesis goes on in them? Or is something else more dominant which gives them their distinct colours. If so what usually is that something? Does the red or yellow autum leaves suggest their photosynthetic abilities have died? So does that colour suggest death soon for these leaves (i.e. sign of old age)?