I am not really expert in this, but I have a couple of books which give a clue.

Philip Haythornthwaite's "Uniforms of the Retreat from Moscow" has an illustration on Plate 13b of a Sergeant Major of the 4th Battalion 2nd Line carrying a battalion fanion. It has a spearhead finial. The description on pages 113-114 states that 1st battalions had red flags with horizontal blue stripes at top and bottom edges, 2nd battalions - blue flags with horizontal red stripes at top and bottom edges, 3rd battalions - three red and two blue alternate stripes of equal width, 4th battalions - red and blue vertical (sources vary as to whether the red or blue was closest to the staff) and 6th battalion - two blue and one red alternate horizontal stripes. It does not mention 5th battalion. On all fanions there was an upper line of lettering "2me REGT DE LIGNE" etc and lower line of lettering "1er BATAILLON" etc.

John Elting's "Swords Around a Throne" states on page 348, that from 24 November 1811 a new system was ordered of battalion fanions of 2nd battalion - white, 3rd battalion - red, 4th battalion - blue, 5th battalion - green and 6th battalion yellow (with later 7th battalion - violet and possibly 8th battalion - sky blue, for those few regiments with that many battalions). I have read elsewhere that this new system was not introduced until after 1812, hence the description of the red/blue fanions above.

Rod