Del, just found this text on the ACO website, may if we rephrase it a little...
"One of the innovations this year is the 'leader light' system where each car must have 3 LED lights mounted on both sides. This will be familiar to those of you who follow the American Le Mans Series, but is new to many of the European teams this year. Each class has lights of different colour, three for each car; red for LM P1, blue for LM P2, green for LM GT1 and yellow for LM GT2. The leading car in class will show one light, the second place two and third position three lights, so that spectators can more easily follow the progress of the race."