The French were aware that their traditional (mid-19th century) red trousers were not appropriate for modern warfare. Unfortunately, getting them replaced was not an easy task due to political difficulties. This article (in French) is a good summary of the French army's efforts from 1903 to find a uniform more suited to modern warfare: http://rosalielebel75.franceserv.com/reforme-uniforme.html It does mention the importing of red dye from Germany, in the context of the planned future uniform being a patriotic mix of red, white and blue, and the red being omitted due to the supply being curtailed.