Modified mini/usb/ to usb cord to directly charge battery--4 colors but no black!??? Help!

[AC Question]

I want to try using a (cut) modified mini usb/usb cable to directly charge the battery of my old flip phone (Verizon VX 5200). (I don't have the big fat chip size charger.) But when I strip the (mini/usb) end of the cord to expose the wires, there are 4 colored wires, red, white, yellow and green, but NO BLACK!What's the deal with this? Is the cable I intended to use only a data cable and not a charging cable, or does another color act as the black negative wire in this instance> Thanks in advance. And, yes, I will be careful if I can first figure out the answer to this question. Thanks in advance. Looking forward to a quick answer as well!