BLUE:

Give way to a faster car which is about to overtake you.

BLACK WITH ORANGE DISC:

Mechanical problems; stop at pit on the next lap.

YELLOW:

Warning flag, be prepared to slow or stop due to an obstruction on the track or a car off the track.

No overtaking allowed until the next flag point.

BLACK:

If shown this flag you must return to the pits on the next lap, and report to the Stewards.

Typically means you have done something wrong, but may be indicating a problem with your car.

RED:

The session has been ended prematurely (possibly due to an accident or obstruction on the circuit).

Slow immediately and return to the pits.

Be prepared to stop.

No overtaking permitted.

CHEQUERED:

End of the session.

Shown only at the start/finish line.

Return to the pits.

GREEN:

All clear, resume full speed.

Usually shown at the next flag point after a yellow flag.