Changing looks: divider highlight color?

This is not an urgent support question.
I post this here since I guess the themes forum should only be used for posting new themes. I am currently trying to create a dark theme, very much like the dark grey office one.

Only problem I ran into: I frequently use these little dividers that show up when you drag an item from the toolbar halfway away from its neighbour (the one that says "start new group") and I cannot seem to find what changes that highlight color. Currently it is almost white which looks ugly on a dark grey toolbar image.
I looked in both Dopus and Windows specific theme settings but I need the name of that thingy. I pretty much changed everything "border" but that wasnt it.

Does anyone know what I am talking about?

Have a look here: Display colors & options

Aaaah, thank you so much! I will read this thoroughly, exactly what I had been looking for.