As for it's green-ness, the bottle states "For you natural life" and a bit below "'Asahi's Green Cola' is made from selected raw materials derived from plants such as fruits, with cola's own dynamism and briskness." What's inside? High fructose grape sugar, sugar, lemon juice, malt extract, and flavors. I suppose in the literal sense, the marketing is somewhat honest. Still, it's a bit of a shill.
As for the taste, it's very light in flavor, high in sugar. In the world of cola, there's the sugary maltiness of Coke, the citrus edge of Pepsi, and the pure kid's sugar fantasy of RC. This one approaches RC.
It just hit the market a couple of days ago. Between the US big boys, Kirin's Cola Shock and god knows what else shoves it's way onto the shelves, Green Cola's got a long row to hoe. Still it's better than Coke Zero. At least it's drinkable. And the big Zero seems to be having a fine shelf life.