The quote was from a French Minister of War, prior to WWI, in response to calls for the French Army to upgrade their uniforms to something more practical. The British Army had adopted the khaki uniform, while Germany had moved to a field gray uniform.
The problem with generals (and ministers of war) is that they tend to be older and hold on to what they learned as they were coming up. Colorful uniforms were actually helpful in the 18th and early 19th centuries in the sense that a general on the field could clearly see which units were where. But as the killing range increased during the Crimean War and the American Civil War, it became better to be less conspicuous on the battlefield. But the old guys couldn’t let go of idea that French soldiers have always worn red trousers.
Even worse was the idea that élan would carry the troops through artillery and machine-gun fire. It took a couple of years of slaughter before that idea was abandoned.