The owner's manuals of recreational vehicles generally include a plumbing schematic that quite often is color-coded. The color code used in the plumbing schematic indicates the type of water flowing through the system.
The plumbing schematic of a recreational vehicle gives an insight into the layout of its plumbing system and can be used to make any repairs or maintain the system. The schematic may be accompanied by a key or legend that indicates the meaning of the colors and symbols used in it.
Generally, blue color in the schematic indicates clean and fresh water flowing in the pipes, gray color indicates pipes through which used dishwater flows, red color indicates the pipes for hot water and black color represents the pipes for sewage water.