Green mobs give ur higher possibility to drop an item when white/orange/red wich gives more exp. It comes like this - 1. Blue wich is 6++ lvls lower then u, wich gives very bad exp and bad drop. 2. Green wich is 4-6 lvls lower then u , wich gives normal exp and more possibility to drop something. 3. White wich is 1-3 lvls lower then u gives also noormal/good exp and normal possibility to drop something. 4. Orange wich is 1-3 lvls higher then u and gives good exp but a smaller possiblity to drop something. 5. Red wich is 4++ lvls higher then u, gives awesome exp but bad drop.
If im somewhere wrong , correct me, cause im not quite sure about orange if its 1-3 lvls higher. And this once told me a player in sro, i dunno if its true, but thats what i heard.