Wikipedia:

The Chasseurs à pied were the light infantrymen of the French Imperial army. They were armed the same as their counterparts in the regular line infantry (fusilier) battalions, but were trained to excel in marksmanship and in executing manoeuvres at high speed.

Following the Napoleonic Wars the Chasseurs à pied continued to exist as a separate corps within the infantry. Initially a specially trained elite, their tactical role eventually came to match that of the ordinary lignards (line infantry). By the late 19th century the differences between the two branches were confined to uniform and insignia, although the chasseurs retained a strong esprit de corps.

In 1914, the Chasseurs went to war in dark blue coat and trousers with yellow insignia on their kepi and collar. In 1916, they were issued a short Dolman jacket and all their insignia changed to green.