White wire is the ground (-) wire in the camper to tow vehicle connection.
Other than that, Jack The Rabbit is correct. It seams anyone running dc wire simply uses whatever they may have at hand.
RED and GREEN felt disks are sold
at battery supply counters to be placed on the + and - terminals of the battery to prevent corrosion. The red should be placed on the + terminal.
Your tow vehicle will have Red connected to the + and a black wire connected to the frame. Then: The actual receptacle for the trailer has a White wire for the - and it could also be connected to the frame.
It's easy to see why this might get complicated for such a simple subject.
Check your trailer wiring diagram for the specified wiring color.