I understand the green wire in a USB wire is data- and the white is data+the problem is I don't understand what that means. Is data+ the serial signal in both directions and data- is the grounding for that connection? Is so, why isn't all the grounding done by black? Or: Is the data plus from a bigger device to a smaller one and data- a smaller one to bigger one? I.e: smaller one = Arduino board, bigger one = CPU. If so how do you know which one is the larger device and which one is the smaller one? I.e: a computer plugged into a tablet.