trailer grounding

well all of the auto grounding and most other things i have seen is black. my RC cars, the battery. so why is trailer wired like a house? i have done electronics , computer, network ect school 2 year. i guess some people want their system like they want it. after all remember the electrons do know the wire color. LOL LOL LOL. but what color is the BIT BUCKET should be? LOL LOL LOL.