The rules were that the races were done in the country of the winner of the year before. The races were between national teams. Because of this, the national racing colours had to be set for each country. Great Britain had to choose a different colour to red, white or blue (the colours of the flag) because they had been taken by Italy, Germany and France. They choose shamrock green because the race that year was run in Ireland. This became known as the British racing green.