Version: (using KDE Devel) Installed from: Compiled sources OS: Linux Background of the scrollbar is black and arrows do not show when using the oxygen style. (I do not know if this is the right place to report oxygen related bugs but I cannot find other way to report it in bugs.kde.org.)
This is something that both myself and at least one of the Oxygen style developers are aware of. We do not have an agreed solution at present.
I can confirm this problem.
Fixed recently in SVN. The area of the terminal display behind the scrollbar is filled with the scrollbar's background colour - which produces the correct appearance.