The blue tape indicated the area of most color concentration across the width, and the designer wanted that area to be at around eye level on the finished panels.
My biggest concern was how to control take-up from sewing the flange and facing to the face. To mitigate that as much as possible, the flange was hand-basted in to place before being machine-sewn. Those cutoff strips from the inset pattern match were not wasted- they became the facing for the lead edge side hems.
I haven't seen this treatment yet in its new home, but I did see the really cool Houles tiebacks chosen for draping the panels!