There is no deep dark mystery about DC color codes. I'm not sure where the decision to use white for ground came from, but it has been like that on every trailer I have seen, except those rewired by shade tree electricians. Then it's anybody's guess.
In the marine industry, the standard for DC has been red/black, with black always being ground. Several years ago ABYC decided to accept the use of Yellow for DC ground. The rational was that there were too many armchair electricians that were connecting DC ground(black) to AC hot(Black) with disastrous results. Another resin was that while it was discouraged, often AC and DC wiring harnesses were(and still are) run in the same bundle, and the black wires created a lot of confusion. The other multiple colors, both solid and stripe combinations, used in marine wiring are a standard color code also, with specific colors used for engine control, instruments, lights, sensors, etc. I don't know if this has evolved into maritime law as the US Coast hard regulates just about everything in the marine industry. So when you look at a boat wiring harness and see a dozen different colored wires, don't think this were just pulled at random off the wire rack.
To get back to the original topic of RV wiring, the only colors you should ever need for DC are black, or red, and white. If you decide to "roll your own", you are asking for problems as you will probably not make notes of what you are doing and that's not to mention the headaches you create for the next owner.
