its in the scrollbar code for 1001. If you are using Open Live you can disable this line in skininfo.xml by looking at the rectangle replacement section.
If you aren't well then you have to go into the 1001 style and edit:
code:
Scrollbar
{
AccName:rcstr(20194);
AccRole:3;
Accessible:true;
Padding:rcrect(20189);
BorderThickness:rect(0,0,0,0);
BorderColor:rcclr(59504);
}
Scrollbar[vertical]
{
AccName:rcstr(20195);
AccRole:3;
Accessible:true;
Padding:rcrect(20188);
BorderThickness:rect(0,0,0,0);
BorderColor:rcclr(59504);
}
This will remove the line, but if you want to just change the color of it will just edit the bordercolor property instead.
Note that this will only apply to the contact list itself. If you want to do this to all windows then you have to do this to all the style files.