White, yellow and red stakes and lines are common on golf courses. But there are other colors used, too. As we noted in the section on white stakes, white usually means out-of-bounds, but white lines are often used in-bounds to denote ground under repair.
Less common colors seen on golf courses include blue and green. Some stakes can even be multicolored.
"golfrt1" is a rules official who posts in the About.com Golf Forums. He responded to a question in the forums about this very topic, and we'll quote the portion of his reply that deals with less-common colors:
Double Stakes, Yellow Stake Next to Red Stake (frequently tied together)
These denote the dividing point between a dual hazard, treated as a regular water hazard on one side and a lateral water hazard on the other side.
Uncommon, but they are sometimes used to denote ground under repair. (More commonly, GUR is denoted by a white line painted around the area.) Check with your head pro or starter for further information, if not shown on the scorecard or Conditions of Competition.
Rare, used to denote environmentally sensitive areas (ESA). Check your scorecard or Conditions of Competition - ESAs should be prominently posted because entering such areas is often a matter of federal regulation.
Blue Stakes with Green Tops
Under a local rule, designates an ESA being treated as ground under repair with mandatory relief.
Red Stakes with Green Tops
Under a local rule, designates an ESA being treated as a lateral water hazard with mandatory relief.