The green glass preserves the nectar, just like the green glass preserves Italian olive oil!  The green glass also inhibits mildew growth in the bottle.  Mildew is bad for the bird, and very hard to clean.  Unlike a glass feeder, plastic feeders will leech a bad plastic taste when it sits in the sun.  The metal bottom does not leak, rust or fade. It is easy to fill;  turn it upside down and unscrew the metal base.  There is nothing on the inside of the bottom reservoir for the sugar to stick to so it does not get crusted with hard sugar.  Wash with hot water.  Do not put in the dishwasher.

Indian Paintbrush Hummingbird Feeder