The main objective of the yellow lights (used first in military vehicles) was not to be such an easy target.
The Government enacted a law on the 3rd of November, 1936 stating that all vehicles put into production in 1937 are required to have yellow headlights. The French being who they are, didn't abandon these headlights until 1993 when forced by the European Unions conformity standards.
http://www.french-cars-in-america.com/why-did-france-have-yellow-headlights
