I found this post on the web:
Red Flag: The Soviet Union has returned and the turn is suspended. All the drivers should pass through pits and verify their membership to the Communist Party. (I knew that this of the single-engine was a little Pinko...)
Yellow Flag: Danger on the track, the Simpsons were authorized to race.
In the sector signalized with flag is prohibited to overpass, except to drivers with liver emergencies.
Surface Flag (Red and Yellow Stripped): Benvingut a Catalunya.
Green Flag: Greenpeace activist have come to stop the race in order to destroy the circuit and build in his place a tofu factory.
Blue Flag: Drivers are allowed to consume Viagra in limited quantities as long as let who comes in his flying lap pass through.
White Flag: Anthony Sullivan and Ron Popeil are moving really slow through the track defying everyone to see which laundry powder gets the clothes more clean white.