I know nothing of the FFL but I'm really interested in gaming with some.
Can someone in the know quickly explain in what theaters the different uniforms are present? 
The Artizan range was primarily designed to depict French troops during the North African campaigns which took place between 1899 and 1914, and it's probably the most comprehensive range of figures on the subject at the moment. The main theatres of operations were the
Sud-Oranais (i.e the region which straddles the Algerian-Moroccan border) and Morocco itself. The
légionnaires in shirts are more suited for the
Sud-Oranais campaigns of 1900-1907 : the men fought in shirtsleeve order during the day but wore their blue greatcoats at night as protection against the cold. Headgear was officially the
melon sun helmet, but covered kepis with a neck curtain were also commonly used.
The 1907-1914 Moroccan campaigns were fought in two main dress orders : either the dark blue/grey greatcoat worn with covered or uncovered kepis and white fatigue trousers (the classic foreign legion look), or the M1901 colonial troops khaki uniform which began to be distributed to the Legion circa 1907-1908. By 1909, all front-line units in Morocco had apparently received the M1901 jacket which could be worn with either khaki or white fatigue trousers. Sun helmets could be white or fitted with a khaki cover, the latter being seemingly more common. That said, period photos also show French soldiers in Morocco wearing white shirts and kepis with a white cover but not neck curtain.
Incidentally, The
légionnaires in M1901 khaki jackets and sun helmets can also be used for the post-1900 Tonkin/Indochina campaigns.