Because electrically, in the AC world, unless it's controls GROUNDS MUST BE EITHER BARE OR GREEN- per NEC we must follow as electricians. What color is the ground outside? Green. What does the ground wire do? Provide a safe path to ground. Where does that path end? A 6 ft rod, usually x2 spread 10' apart with a continuous connection (no splicing allowed), driven into the ground. ONLY low voltage wiring can use green as anything that's not a ground, but even then it's extremely rare to see an all green wire as anything else. Even green/------- stripe is generally used in control circuits where something like a relay closes something to chassis ground. Like white can't be used for anything besides a neutral, or grounded conductor, can't be white or gray in high voltage. Where black is the most common color for a hot, or ungrounded conductor, no matter what the voltage or phase grouping. Basically, it's common sense to anyone who works with electricity for a living. Even in DC circuits like bikes, you don't find straight green hots. If it's green hot, it's being controlled by a relay of delivers a specific resistance, current, wattage, or voltage which is controlled elsewhere and essential for property function. It's a control wire then. On something with R/YL/YL/YL/GN, you obviously have main power, regulated power X3, chassis ground/negative. But I'm an electrician, later electrical engineer, and been wrenching my whole life, and building customs bikes, cars, trucks a couple decades, and went from buying my first SeaDoo to 3 years later being a certified mechanic and opening a shop and Marina here on a sport lake in Michigan. So there's your answer on green, in long form. Cheers mate.