I don't remember the color (I think it's white) but if you've got the trailer light connector on your rear bumper, it shows which wire is the reverse wire on the lid.. That's what I used as a reference to connect the reverse lights on my tailgate light bar... I'm 99% sure the back up lights are the center connection
The reverse light wire is White/Red. This is available on 34 pin connector C322 located along the frame on the drivers side near the front edge of the drivers door, and just happens to be pin #34. It is also available at the TIPM on Black Connector C6 (might be marked 'F') Pin 5. There is a splice point (S120) between the TIPM and C322. The splice is located behind the drivers kick panel, about 6" from the floor.