The American Public Works Association (APWA) recommends the following guidelines be used when marking underground utilities.
||Pink = Temporary Survey
||Red = Electric Power Lines, Cables,
Conduit and Lighting Cables
Gas, Oil, Steam, Petroleum or Gaseous
Communication, Alarm or Signal Lines,
Cables or Conduit
Reclaimed Water, Irrigation and Slurry
Sewer and Drain Lines
Why are these colors used?
Often, you will see these colors used to identify
utility lines in cities and on a university campus.
Sometimes city or campus utility departments will
paint the tops (such as manhole lids, or sewer
drop-inlet tops) of their utilities these colors
before an aerial survey is flown so that the people
creating the maps can identify the type of utility.
If you see utilities being painted in your area,
there's a good chance an aerial survey is going to
be flown soon. Or sometimes utility departments are
just taking inventory of their assets and are
painting to identify their utility infrastructure,
or possibly to diagnose a problem and they need to
identify multiple utility types in an given area.
The utility departments that mark their utilities
usually use inverted spray paint, also known as
"upside down paint". EngineerSupply sells inverted
spray paint by the case.
Inverted Utility Marking Paint here