Here's the link if you want to have a look : They're the fab green uniforms (with higher officer wearing their blue Middle Guard uniforms)
The uniforms are based on research in a newish book Dawson's Napoleon's Imperial Guard the Infantry.
From this it is clear that the flanqueur's uniform was green with chamois facings.
Chamois was also the facing colour for voltigeurs in the line, and is a distinct
colour of a pale yellow/beige shade, as opposed to the yellow used by the voltigeurs
of the Guard. The only scarlet cloth issued was for the tail facings and linings in milled serge.
Therefore, Knoetel and Jouineau are wrong in ascribing scarlet piping. The facings
of the tails were clearly scarlet milled serge with chamois piping. The regiment's
archive confirms what the period iconography shows: chamois collar and cuffs.
So rather than having green cuffs piped yellow (or red) they are painted with yellow - or chamois cuffs.
There's a wonderful representation of these units over on this blog, where they also chose to represnt officers in green too - so effectively only low ranking officers.