What color flag tells Formula One drivers to let a faster car pass?

A blue flag tells Formula One drivers to let a faster car pass.

In a race, the signal most commonly applies when a faster car is approaching a slower car that is about to be lapped. The slower driver must facilitate the pass at the earliest safe opportunity rather than defending the position as though it were a normal battle for track position.

Blue flags can also appear outside the main race context. For example, a driver on a slow cool-down lap in qualifying may be warned that a car on a fast lap is approaching. Modern Formula One also supplements physical flags with blue lights, cockpit indicators and timing-screen messages.

The other options have different meanings: yellow warns of danger and requires caution, green signals that a hazard has cleared, and black orders a driver to return to the pits or indicates a disqualification. Blue does not mean the race has ended; that is the chequered flag.