When should I show the blue flag, the white flag or the slippery-surface flag?

From MSA Appendix H (2026):

Blue flag. Show it:

• when a competitor is obviously obstructing;
• when slower vehicles are being lapped by the leader;
• when a faster vehicle making up time is working through the field.

It is not needed on the first lap while the field is still bunched, when two or more drivers are racing wheel to wheel over several laps, or when a driver clearly knows they are about to be passed. Use it with discretion; in the wet with poor visibility it is often the best warning.

White flag. A service vehicle (ambulance, etc.) or a slow competing car. Wave it while the vehicle is in your sector, then hold it still until the vehicle reaches the end of the next sector. If the vehicle stops on track, replace the white flag with yellow immediately.

Yellow with red stripes. Loss of grip from oil, water or similar. With a hand pointed at the sky it warns of a local rain shower. Show it for 2 laps or until the surface is back to normal.

A portable fire extinguisher can be shown to a competitor whose vehicle appears to be on fire.