Pipe markings are standardized identification marks used on pipes to identify contents and flow direction. They are particularly important to the complex systems of piping found in the engine room, but may also be carried over into drawings.
The most common standard is the ANSI/ASME joint code 13.1, currently in the 2007 revision (13.1 2007). ISO 14726 is another popular standard, now in the 2008 revision. Pipes will be marked with bands of the designated colours, and may be combined where carriage overlaps (i.e., firefighting fresh water). As these standards are pretty general, additional colours will be used as necessary (and properly documented).
Outside the standards, ships may adopt internal conventions for markings. Some other common colours found aboard ships include;