What was the whole point of blue uniforms in WW1? Wouldn't they just give away the positions of French troops?

Red Pants Problem

When World War I began in 1914, French soldiers had dark blue jackets and very red trousers. Army already realized that soldiers were clearly visible in the red pants but the politicians were unwilling to change it. There was one extreme statement even, of robbing France of the red pants to the effect that this would destroy France. So soldiers went to battle in wearing apparel seen at a distance.

Credit: Google

The New Uniform

At the start of the war, the number of soldiers who died was very high forcing the army to switch to new uniforms. They immediately had a dull brown-purple in mind to use. That, though, required special red dye manufactured in Germany. France could not get it as they were engaged with Germany in the war.

They had only blue and white dyes, so they combined them and they received light blue-gray colored dye trademarked as Horizon Blue. This was not the paint choice to conceal the troops- it was simply the fastest color available. Eventually, French soldiers were painted blue due to recalcitrant commanders and an issue in supplies.