There are many green objects. For example, grass, leaves, buoys to starboard, David (according to Stephen), mouldy turds, pea soup, pee soup, everything (when wearing green-tinted spectacles), frogs (not in liquidizers), anything red (if you're colour-blind) absolutely sod-all (if you're totally blind, or else a fool). The Gopsi garden would be green, had it any plants in it.