In the 1805 period battalions carried two flags. The grenadier (first) battalions carried the single white (cross) pattern and a colored pattern. The other battalions carried two colored patterns. There was no "regimental" flag.
At this time, the grenadier battalions of grenadier or musketeer regiments were distinguishable only by their facings.
I try to keeps notes on these common questions at: zaotlichiye.net63.net/allfacings.html - however I will caution that it's best to be familiar with Conrad's translations first.
"Puce" is a (rare) mistranslation. It should be "poppy".
Although evidence is sparse (mostly that no one notes otherwise) Russian flags appear to be double sided, so each side was identical. That would make one of the two illustrations of the Leib-garde white pattern incorrect. My best guess is that the first illustration (Parkhayev?) is incorrect and the second, Viskovatov, is correct.
A similar question involves the eagle. Viskovatov shows the eagle raising its wing to the fly and lowered towards the hoist. The surviving Duc de Borbon relic shows the same. However the Leib-garde relic recently auctioned by Sotheby's shows the eagle raising its left wing on both sides.
Finally, the Maltese crown depicted on the guard pattern was a guard distinction and absent on line flags.