That white bar/shadow/line near the top shows up when I set the icon size less than 45 px. In this case, it is set to the minimum value of 32 px. This is part of the dock and not the background. Looks like a bug to me as it makes no sense why that bar would be there.
Style/Color is set to "Aero #1". That appears to be the default style in ObjectDock Plus v2. "Aero #1" is the only Aero option I see.
You are correct, I have two separators in there. The separators just don't have a graphic appearance that I like, so I was hoping for a way to change the graphic.
When you ask "which dock is it?", I don't know what you are asking. It's the only dock I have and is a "tabbed dock." Here's the Settings screen: