At least as late as the Battle of the Frontiers in August 1914, the very first actions of the First World War, the French Army advanced into Alsace-Lorraine with the regimental colours flying and the band playing. Buglers, incidentally, are disproportionately represented in French war graves from those battles. The French Army suffered a worse casualty rate in a single day that summer than the British Army would later do on the First Day on the Somme. This is also, incidentally, the same battle where the French infamously advanced in powder-blue tunics and red trousers: the camouflaged bleu-horizon uniform had been officially adopted at that time but had yet to reach many units. Red trousers, blue jackets and billowing flags were swiftly abandoned shortly afterwards.

Sources:

Max Hastings, Catastrophe: Europe Goes to War, 1914