white border/ box around TLB stand alone bars

yes, I use WindowBlinds and tried both, skinning for tlbHost dis- and enabled, quit and restarted tlbHost. The look of the bars did change but no change in terms of the border, so it is not WB responsible for that. Also restarted Windows Aero as admin via net stop uxsms and net start uxsms, and again, no change.

The screenshot (left part) is already at the top, just envision it expanded and mirrored to the right (+ a dark background around to see the border).

So is there any spot in TLB where toolbar border thickness can be adjusted?