Two different studies indicate that bright yellow and bright blue are the most visible colors for a car.
The University of California found that of the two colors, yellow shows up best at night, blue in fog and daylight.
A test by Mercedes-Benz same conclusion, but came up with the suggested that white might be even better than blue and yellow except in snow and white sand.
The worst colors for visibility, day or night, are grey and dark green.
Car and Driver reported pink the best for day/night.