In a way or other, the Pre-Pro #3 suit is the bonding link between the Pre-Pro #1 and ESB Hero suits. The Pre-Pro #3 has the same gauntlets and jetpack from the Pre-Pro #1 suit, while the ESB Hero has the soft parts and the shin tools from the Pre-Pro #3 suit. The main link between these suits is the same color scheme used on the armors and helmets (especially the Pre-Pro #3 and the ESB Hero).
Maybe that had to switch some out? None of the screen shots I looked at had a grey one...I was looking at the HD screen captures though, and they all look white to me...I could be wrong, though.
It seems that all the images with the grey stud are from the hallway scene and the other scenes are with the all white studs (except the one red top stud):
Whatever stud combination you use (3 all white and 1 white with red top or 2 all white, 1 white with red top and 1 all grey) is screen accurate.