Since the 1920s, Italian race cars of Ferrari were (and often still are) painted in "race red" (Rosso Corsa). This was the customary national racing color of Italy, as recommended between the World Wars by the organizations that later would become the FIA. In that scheme, French cars like Bugatti were blue, German like BMW and Porsche white (since 1934 also Silver Arrows), British racing green etc.
Curiously, Ferrari won the 1964 World championship with John Surtees by competing the last two races in cars painted white and blue, as these were not entered by the Italian factory themselves, but the US-based NART team. This was done as a protest concerning arguments between Ferrari and the Italian Racing Authorities regarding the homologation of a new mid-engined Ferrari race car.
Aston martin is mostly seen silver because it looks goood and is like that in the movies. However it should be http://en.wikipedia.org/wiki/British_racing_green
Mercedes-Benz, Auto Union, Veritas, Borgward, EMW, Porsche, Audi are http://en.wikipedia.org/wiki/Silver_Arrows