The American Public Works Association (APWA) Uniform Color Codes for survey marker temporary marking of underground utilities:

Red Electric Power Lines, Cables, Conduit, and Lighting Cables
Orange Communication, Alarm or Signal Lines, Cables, or Conduit
Yellow Gas, Oil, Steam, Petroleum, or Gaseous Material
Green Sewers and Drain Lines
Blue Potable Water
White Proposed Excavation Limits or Route
Pink Temporary Survey Markings, Unknown / Unidentified Facilities
Purple Reclaimed Water, Irrigation, and Slurry Lines